how does the feudal relationship work when a vassal has titles in multiple kingdoms? do responsibilities to multiple monarchs become hierarchical in some way, or do you just have to balance all of them?

Well to explore a pure hypothetical…What happens when a vassal in one realm becomes a sovereign in another? Is that vassal still a vassal? Or are they an equal monarch?

Ok, just for the sake of argument, let’s call the vassal Filliam of Schnormandy…no, that’s too obvious, how about Kenry the Second of Hingland…no, still too on-the-nose, ok, how about Nedward the Third Kantagalant?  

But seriously folks…the answer is it doesn’t and you get wars for hundreds of years, some very unkind words about national cuisine, hygenie, and culture, and then a lot of nationalist slap-fighting at international meetings for a couple more hundred years.