Your court consists of all your direct vassals, The people you draw to your court through invitation or marriages, your children (or siblings/uncles/etc) who are not married off into another court or given land of their own. If they are given land, they may still be in your court if they remain a direct vassal. Generally, I try to get rid of any 'unhappy' courtiers right away unless they have worthy skills. Anyone with an oppinion of under 50 I get rid of so I don't need to worry about being killed. I will lure in as much as possible characters with high martial skill just because it's always good to have 5 or 6 men with high martial skill to lead your personal levies, and you might not want to risk having vassals lead your troops because of troubles that might result if they die. I also try to get at least 1 20+ stat person in each category so I have quality people in my council. I will typically try to mary all males in my court with genius or sharp females so they can produce genius or sharp offspring who will be raised to have the correct skills and culture. These will then be wed into my dynasty and some may be given minor holdings which keeps them as my direct vassals. In this way, I always have a few good marriage choices for my hiers on hand.