Factions and their demands against my family

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I am playing as Byzantium now and I just noticed strange thing about AI. Problem is serious when AI player got more than one king titles. In my game my family united few thrones - first was Hungary and Poland what made really strong realm who blocked HRE from East. Second was Ruthenia and Rus - this realm was so strong that even menage to stop GH. And now, there is a problem. In spite of the fact they had strong position there, they are giving king titles easily when faction demand it. First was Hungary and Poland, they gave away both king titles to really weak families which had weak claims. With my support (Byzantium) they took the thrones again, but then one weak faction demanded it again and they gave away Poland. Similar situation was in Rus / Ruthenia. They gave away one king title, second one was lost due to bad marriage, so I put my family there by force and new queen gained both titles again. When my Emperor died there was a faction in my empire and I gave her independence she wanted. Then she had to face revolt. It was first revolt of Rurikovich, she crushed them, but when she released rovolters they made faction again and demanded Ruthenia. Queen accepted in spite of the fact that she was seriously much stronger than revolters and she had my support. Annoying situation also appeared in Sweden where my family ruled for over 50 years, but faction put imbecil not from my dynasty on throne - in spite of the fact that queen there had 60% of all holdings in this kingdom. Is this really work as it should ? Why those factions are getting their demands so easily... ?