How to Convert People to Religion

The game forces you to choose three noble families for each city. Once you've chosen three of them, the fourth one is locked out forever. Depending on what kind of empire you're making, you'll decide which of the three families you want involved in your empire. You can use different family members who like you to intercede on your behalf with other family members who don't like you and build relationships that way. How do you convert people to religion? You just slay.