Fiefs

how can I take fiefs back from my vassals?
Can i give one of my fiefs to another lord or King of another Realm?

Don't know if theres any more direct way to do it but I just trade some castle I own with his. Though keep in mind the castle or town needs to be worth more or equal for them to accept the trade. The way to make a land trade is to talk to the lord personally. I think to give castles or towns to another faction you need to send an emissary through your main castle.