I've got no problems with Rhaenys having 4 or 5 dragons
I'm more concerned about people taking them when she snuffs it lol.
Aelinor was my son's third wife, it makes sense, under such circumstances for her to bring the egg with her too. Also: adding modifiers for people with trusting/ paranoid traits might make people more/ less likely to bring an egg with them somewhere else. Kind of like how I'm paranoid about dragon's falling out of my House's hands; a character, upon marriage, has a choice to give away or keep their egg to keep it within their House's hands.
For example: If Aelinor had given her dragon egg to her father/ the ruler of Sweetport Sound upon her marriage to my son to keep the egg within her family because she has the paranoid trait. If she had no paranoid trait she is X times more likely to bring the egg with her.
As for the whole war + conquering their lands, could you add changes to that? For example: If you're Top Liege and have Blood Laws active, you should be able to simply demand the dragon egg back. Especially for such a low-ranking vassal, who has little to no real power anyway, I think that seems fair.
As well as a modifier if they are a rival of yours. It makes sense, then, that you'd want to take away any advantage to your rival.