You can join a faction by finding the leader of it. If you have low renown which i expect you do, you can join as a mercenary and fight for the kingdom. Later you can try again to be a vassal, then you can have some lands depending on your influence on votes to receive one.
About having wife/children, find a single woman, woo her, try to give the right answers to her questions and she ll marry you. When you give wrong the chance is gone.
I dont do much trading, someone else can explain that maybe.