I wanted to try and write a decent reply to this and it started getting a bit long so I ended up writing my guide.

it does give you ideas on how to increase your chances of having someone to marry your favourite generals, however there is no definite way to make sure becuase if you keep marrying people in the family they will have 4 kids and your family can expand exponentially and then you will no longer get the event proposal for marriage or adoption into the family until your family isn't as large (a few people kick the bucket) so try to keep your family as small as you possibly can and only ever try to marry your king and faction heir, and then maybe a general you like that has good traits and that way your family tree shouldn't be too overloaded however you will need more generals from time to time but just don't marry too many couples and you should be ok :)