Was Randyll acting within the bounds of the law in forcing his legal heir to surrender all property rights ? Theoretically, could Sam have gone to Highgarden to seek intervention from their liege lord? Do you think there was any chance of Mace standing up for Sam against one of his principal bannerman (& most able general) ?

This is what GRRM has said on the matter:

“Well, the short answer is that the laws of inheritance in the Seven Kingdoms are modelled on those in real medieval history… which is to say, they were vague, uncodified, subject to varying interpertations, and often contradictory.

A man’s eldest son was his heir. After that the next eldest son. Then the next, etc. Daughters were not considered while there was a living son, except in Dorne, where females had equal right of inheritance according to age.

After the sons, most would say that the eldest daughter is next in line. But there might be an argument from the dead man’s brothers, say. Does a male sibling or a female child take precedence? Each side has a “claim.”

What if there are no childen, only grandchildren and great grandchildren. Is precedence or proximity the more important principle? Do bastards have any rights? What about bastards who have been legitimized, do they go in at the end after the trueborn kids, or according to birth order? What about widows? And what about the will of the deceased? Can a lord disinherit one son, and name a younger son as heir? Or even a bastard?There are no clear cut answers, either in Westeros or in real medieval history. Things were often decided on a case by case basis. A case might set a precedent for later cases… but as often as not, the precedents conflicted as much as the claims.”

Keep in mind, Randyll Tarly wasn’t proposing to write a will that bypassed Sam in favor of Dickon, or any such legal manuever. He was straight-forwardly threatening to murder Sam if he didn’t comply.

So yes, potentially Sam could have gone to Highgarden and protested that his father was not only breaking the laws of inheritance but was an attempted kinslayer and murderer on top of that. I doubt that Mace Tyrell would have been particularly interested in championing Sam’s claims, however.

Is westeros following civil or common law?

Great question! It seems like a bit of both:

In these progresses, the king was accompanied not only by his courtiers but by maesters and septons as well. Six maesters were often in his company to advise him upon the local laws and traditions of the former realms, so that he might rule in judgment at the courts he held. Rather than attempting to unify the realm under one set of laws, he respected the differing customs of each region and sought to judge as their past kings might have. (WOIAF)

However, these traditions were then blended in with new decrees from the Iron Throne into a common law; for example, see “The “rule of six,” now part of the common law, was established by Rhaenys as she sat the Iron Throne while the king was upon one of his progresses.”

In the reign of King Jaehaerys I, this changed:

“With Barth’s aid and advice, King Jaehaerys did more to reform the realm than any other king who lived before or after. Where his grandsire, King Aegon, had left the laws of the Seven Kingdoms to the vagaries of local tradition and custom, Jaehaerys created the first unified code, so that from the North to the Dornish Marches, the realm shared a single rule of law.” (WOIAF)

As I’ve said before, it’s entirely unclear how this legal code is enforced, or how this code brought the different legal traditions of seven kingdoms plus the accretions of two generations of Targaryens into harmony. However, it’s quite likely that the previous “common law” was the foundation of Jaehaerys’ Code, which was revised in the reign of King Viserys II.

How much can Daeron be blamed for the Trial by Seven at Ashford and its disastrous fallout? To be sure, Aerion was the party most responsible, but had Daeron not been a drunk and a craven and had he not accused Dunk of kidnapping Egg, Aerion would have had no pretext for a trial by seven.

Not really.

“Aerion has already filled his father’s ear. And Daeron has not helped you either. To excuse his own cowardice, he told my brother that a huge robber knight, chance met on the road, made off with Aegon. I fear you have been cast as this robber knight, ser. In Daeron’s tale, he has spent all these days pursuing you hither and yon, to win back his brother.”

“But Egg will tell him the truth. Aegon, I mean.

“Egg will tell him, I have no doubt,” said Prince Baelor, “but the boy has been known to lie too, as you have good reason to recall. Which son will my brother believe? As for the matter of these puppeteers, by the time Aerion is done twisting the tale it will be high treason. The dragon is the sigil of the royal House. To portray one being slain, sawdust blood spilling from its neck … well, it was doubtless innocent, but it was far from wise. Aerion calls it a veiled attack on House Targaryen, an incitement to revolt. Maekar will likely agree. My brother has a prickly nature, and he has placed all his best hopes on Aerion, since Daeron has been such a grave disappointment to him.” The prince took a sip of wine, then set the goblet aside. “Whatever my brother believes or fails to believe, one truth is beyond dispute. You laid hands upon the blood of the dragon. For that offense, you must be tried, and judged, and punished.”

“Punished?” Dunk did not like the sound of that.

“Aerion would like your head, with or without teeth. He will not have it, I promise you, but I cannot deny him a trial. As my royal father is hundreds of leagues away, my brother and I must sit in judgment of you, along with Lord Ashford, whose domains these are, and Lord Tyrell of Highgarden, his liege lord. The last time a man was found guilty of striking one of royal blood, it was decreed that he should lose the offending hand.”

(Emphasis mine)

Daeron’s self-serving lie didn’t help matters, but Baelor makes it quite clear: Dunk striking Aerion is a separate legal matter from whether or not Dunk kidnapped Aegon, and there would have had to be a trial by combat.

Making that trial a trial by seven was “my right, I do believe.“ Daeron not having made his contribution would make it somewhat more politically embarrassing for Aerion to claim that right, but he always had the perogative to “insist upon a trial of seven.”

How could you make Westeros more democratic, or meritocratic, without pushing the nobility into rebellion? Give more power to Guilds maybe, let cities and their urban classes become more wealthy/powerful?

Well, democratic and meritocratic are not the same things; got to be careful when thinking about virtues and political systems, because a lot of people from 18th century liberals to the present day fox themselves by blurring those categories.

So I’m torn between my Team Smallfolk side and my historian’s side. My Team Smallfolk side says we go full Wat Tyler, let the nobility rebel, and then crush them like we’re Flemish artisans. My historian’s side says that revolutions can go backwards and that change is often gradual and long-term (but also that it often goes in a process of “punctuated equilibrium” where you have to push as far as you can in the moment, but always being careful that you push for what’s sustainable).

I would say that you build on existing institutions:

First, institutionalize the Great Councils of Westeros, as a quasi-representative body that embodies an alternative principle of legitimacy beyond the right of blood or conquest, and which seems to operate under the principle of all lords being equal (that’s something you can build off of. (Likewise the Kingsmoot, the elections of the Night’s Watch, etc.) Eventually, build the Great Councils into something akin at least to the Tudor Parliament if not yet at the level of the Parliament of the 17th century.
Second, extend the tradition of “any knight can make a knight” and the quasi-revolutionary nature of the knight’s oath. On a cultural level, encourage storytelling about Ser Duncan the Tall and other knights who expressed their virtues by defying their superiors rather than obeying them. Expand the class of knighthood down into the elite of urban society by making guild masters, burghers, etc. knights. This should create a class of people who have something to lose from the old order coming back, who can mobilize other people to fight counter-revolution. Eventually, give all knights representation on the Great Councils – although the principle of “one lord, one vote” might have to shift to something more elective, because getting everyone in one room is hard enough already.
Third, restore the reforms of Aegon V, whatever they may be. Really work on enforcement, so that the law is uniform whether it’s under the king’s eye in the Crownlands or out in Dorne or in the far North or out in the Westerlands. Work to extend royal justice vis-a-vis the right of pit and gallows, perhaps compromising with the local lords by letting them recommend candidates for justiceships. Eventually, work to expand the idea that individuals and communities have inalienable rights – perhaps building off of the ideology of the Seven that we’re all children of the Gods, etc.

“A personal loan would be different from a loan from an institution of dubious legality, no? ” I don’t mean this as a ‘gotcha’ or anything, I’m asking because you’re the expert. Fundamentally, what’s the difference between house Lannister giving personal loans vs house Lannister establishing a bank and the bank giving personal loans?

The difference is whether we consider the bank a legal entity in its own right, one that can enter into contracts, sue and be sued, etc. Even today, with quite liberalized systems of general incorporation laws as opposed to requiring charters to incorporate, you still need to file paperwork to establish an LLC or an NGO or the like.

So to give a modern analogy, let’s say I decide to open a bank – I rent some office space, hire some people to help me run the bank, put out a sign saying “Bank of Steve now open,” etc. If I don’t do the paperwork to establish the bank as a formal institution, I’m going to have some serious trouble if someone defaults on a mortgage, because the “Bank of Steve” can’t sue someone in court and the defaulter didn’t borrow any money from Steve Attewell personally.

Moreover, banks do more than just give out loans. They also borrow money and invest money, they own real estate and other forms of property, they act as depository institutions, they act as financial middlemen, and so on and so forth. You need some legal framework to legalize these functions and to formalize how disputes that arise from these functions could be resolved.

So in the Westerosi context, without a royal charter that sets out the structure, rights, privileges, and limitations of the Bank, there’s no way to resolve major questions like: can the Bank own land? Who owns the lordship of that land, since “nulle terre sans seigneur”? Can the Bank be summoned to fight for the liege lord of that land, and can it be convicted of a felony if it doesn’t show up? (Likewise, can the Bank summon people to fight for it, and can it convict people of felonies for not showing up?) If someone who’s defaulted on their debt dies, does the Bank inherit their land or the eldest son of the defaulter?