I'm probably not the best person to give advice on this, but I'm constantly dealing with issue with one particular co-worker and she is a Christian too.
I pray daily, before I come into work. I smile, even though I know some of the things she does are spiteful and harmful to others. The meaner she is, the kinder I am to her. Most importantly, I NEVER let her see when she has upset me. I refuse to give satan any glory. Glory belongs to God.
Remember God is just. You don't have to fight your own battles. God will do it for you. Just continue to pray for them, not to change them, but to ask God to change the way you veiw them, and help you deal with them. Delberately be nice to them.