You’re overthinking it. Yoren’s a decent person, and made a moral decision, that’s it. It’s definitely not Varys, since he didn’t know where the hell Arya was and was quite focused on trying to save Ned. 

No, I think he’s just really bad at his job. 

I think there were a number of factors: 

1. The passage of time. After thousands of years with no White Walker attacks and increasingly spaced out wildling kings, the Night’s Watch seems less necessary. 

2. The establishment of the Iron Throne. Previous to the Targaryens, there were a lot more wars both between and within the Seven Kingdoms – which means you have a lot of prisoners after the wars who are rather inconvenient. Highborn might get ransomed, but it’s easier to ship the smallfolk up to the Wall and let someone else feed them. With the Iron Throne providing a continental state and increased peace and security, there’s much less prisoners to take because you have fewer wars and a judicial system to process people through. 

3. Interaction of inability to reproduce and capacity to produce.  Because the Night’s Watch have sworn oaths not to have children, you have to keep replacing members of the Night’s Watch or you start to decline. Moreover, since a third of the Night’s Watch is primarily engaged in feeding the other two thirds, when you start to lose men, you lose the manpower necessary to grow the food you need to keep your target number of men alive. 

4. Institutional weakness re recruitment and training. As I discuss in my exploration of Jon’s chapters in AGOT, the Night’s Watch doesn’t do a very good job recruiting people and training them. Yoren and his two fellow wandering crows simply don’t grab enough men to halt the natural decline in the Night’s Watch’s numbers, let alone reverse that trend. Moreover, there’s a huge bottleneck when it comes to training – Ser Alliser isn’t graduating enough people to make up for natural losses, and is not providing good quality training either. 

From the way that Targaryen succession seems to have worked following the Great Council of 101 AC and the aftermath of the Dance of the Dragons, yes Robert is the legal heir to House Targaryen after the death of Viserys, although Dany would inherit before Edric Storm and probably before Shireen (although that’s something of a tiebreaker scenario). 

Having Stannis or Renly marry Rhaenys would potentially cause a succession crisis: who inherits after Robert, Robert’s kid or Renly/Stannis’ kid w/Rhaenys? 

I think the close-ups were more about Dany finally accepting Jorah back, not the greyscale. Also, I don’t think Jorah touched his own greyscale. He’s looked at it, but didn’t touch it. 

You mean a King Ralph scenario? 

Depends on the politics of the situation, but the rules of Targaryen succession would say that the nearest male relative would inherit, which would have been Robert Baratheon. 

A couple things:

1. Aegon III took over in the aftermath of a very ugly and protracted civil war, and a good bit of his reign was spent trying to make sure it didn’t start up again. Hence, marrying Aegon II’s daughter to try to unite those dynastic claims. Retroactively declaring Aegon II’s decrees void stirs up a lot of trouble, both by offending Aegon II’s partisans and by pissing off people who’ve relied upon royal decrees and legal judgments that are suddenly called into question. 

2. Stare decisis is really important in any system that relies on precedent. If Aegon III can undo the decrees of Aegon II, he’s got to worry that some king who comes after him undoes all of his decrees. 

Probably Randyll Tarly, then Addam Marbrand (although no one’s seen him since he went chasing the Blackfish), then Garlan Tyrell (who’s going to be busy in the Reach), after which you’re really dipping into the junior leagues. 

Moreover, there’s some major problems for any general:

1. Territory vs. Manpower. The Tyrell host already split in half, with 30k going with Garlan to the Reach and 30k staying in the east. That latter 30k is also split between Tarly and Mace who are now in the capitol, and Rowan at Storm’s End. The Lannisters only have 1,000 men on Dragonstone and around 2,000 in Riverrun, the remaining were demobilized after Tywin’s death. With Garlan’s 30k busy in the Reach, that’s 30,000 to deal with everything else – the Riverlands, the capitol, Storm’s End, Dragonstone, etc. 
2. Chain of Command. In the Riverlands, Jaime’s supposed to be in control, but he’s gone missing. Daven has an issue of rank and not being prepared for independent command, as we saw with the 2nd Siege of Riverrun, plus he’s distracted with his wedding. Marbrand hasn’t been seen in a while. If Daven goes, all you have are Freys. Over in the east, Mace has rank, but Tarly has experience and presence, but…
3. Politics. Mace isn’t moving until Margaery is declared innocent. The Tyrells and Cersei are in an undeclared state of war. Gods only know who the Faith Militant or the Goldcloaks will back if it comes to blows. The Golden Company has secret friends in the Reach. If Tarly is one of them, the whole edifice could collapse with a mere nudge.