With regard to point 2;

ages ago I was in a Russian campaign, middle period. I had an empire spanning most of Europe and no problems with loyalty anywhere. My King died at the age of 80 without a son, for some reason, but 5 brothers. A brother became King and at age 76 also had no sons. Pretty much I had no chance!

But the funny thing is, when he died a civil war began, on one side, much much larger was all the surviving brothers bar one(all 8 star generals), supporting Grand Prince Yuri (age 21 or something) who I'd never seen before. On the other side the final brother also called Yuri with very little support. So I'm not sure, if there was no heir in real life a cousin would be found, or an uncle or somebody with royal blood. My point is that there are lots of generals floating around with royal blood so maybe it sparks off a civil war between the ones with the most influence/least loyalty?