How does a dynasty work

Ou can place your dynasty (or have their dynasty) at the head of another country by royal marriages. When you mouse-over other rulers it will show you what royal marriages they have in place and what will happen if they die. If they do not yet have an heir there is a possibility that your dynasty will assume the throne. It will say something along the lines of: a noble of the house of [your dynasty] will assume the throne. Other possibilities include a PU or other royal houses taking the throne. Someone here will have to correct me if I'm wrong but prestige plays a big part in which house will take the throne so having high prestige will increase the odds of having your dynasty take power.