Muslims believe apostasy (which includes even criticizing Islam out loud) is worthy of death. They have many circular arguments about why it's wrong to disbelieve in anything about their religion. Also, they're really tribal, and would bring shame to their family and friends/community by converting. I hate to say it, but I think they're effectively brainwashed. Just be patient, warn them about what they're doing or not doing and what God has to say about it, then trust that He will do something about it.