First, If they dont like each other, there isn't much you can do tbh. Often, if a player says he don't like some, he will generally be a trouble causer, so get rid of him anyway.
Manager discapline, this can be your media comments,but also how you react to player issues, so if you fined a player for getting 2 yellow cards in one game, and then only warned a player for the same thing in another, then the players dont know where they stand. But in my experience, this issue for a player can lead to loads of problems, so you might want to sell him too | 
