Aggression is often how boys show their feelings of hurt. First, rest assured that most likely they will be best friends as adults no matter how they treat each other now. You really need to stress to the boys how quickly and unexpectedly one of these fights can turn deadly. All it takes is one push where someone hits their head, or one sitting on the other's chest. You want this fear to always be in the back of their head while fighting. I think you first need to have a no tolerance rule in your house. Stress that home is the one safe place in the world, and it needs to be everyone's soft place to fall. You might consider counseling for a little while so they can get some of their issues out.
As for your daughter, make hockey time your "date" time with her. While the boys are playing, make that your time to talk with her or whatever. Also, appoint one night a week or every other week where she can choose what the two of you do together. You can go out to dinner, go to the movies, the mall, or just lie in bed together and watch a movie.
See if your ex can spend some one on one time with the boys when he is in town to. They need to feel like they are loved and seen as individuals, and not "the boys".