The dynasty is very important for every great ruler because there are only 2 ways to create knights - promote them from your dynasty or hire them from the tavern. In Khan Wars every ruler starts with 1 son and 1 daughter and can request offspring from them only after they become knights. When a child is born the ruler must wait for several days for the infant child to reach suitable knighthood age.
The information about the marriage between two players is shown in the player profiles, but most importantly reduces march time with 15%, because the road taxes do not apply. Isn't that a great way to confirm a great union?
If there is more than 1 marriage between two players, that doesn't change things - the percentage stays 15%, no matter how many marriages the players have between themselves. By cancellation of the marriage the marches start to function as before the marriage.
If you announce divorce for one of your knights you aren't allowed to marry the same knight again in the next 24 hours.