J.L.
What I used to do with my nephews was make them stay someplace or so something together until they found a way to get along. Perhaps make them both sit on the same rug; they can not get up until they are no longer fighting. Put 2 chairs or stools in the middle of a room and make them sit there until they find a way to share or get along. Send them to a room (preferably with no tv or computer), same thing...can't leave until they are getting along. Have them make cookies together, set the table together, rake leaves together... When they got a little older, when they started fighting I would stop them & have them tell me something nice or something they like about the other one. If they could not, I would use one of the above until they could. However, they are boys and siblings and are bound to fight and/or get a little irritated with each other on occasion. I would not expect it to ever stop completely, but best of luck to you teaching them to find a way to get along or separate themselves from a situation before it gets out of control. My nephews are much older now and get along fairly well. I have 2 young girls now and will have to wait to see if these work for them too! :)