Hi A.*Ü*
I have 3 boys, but my the oldest is 18 so no problem with him, the other 2 are 13 and 11 yrs old, and they too seem to fight still over things like clothes, toys, games, shoes you name it, and it is not so much as bad now, but when it was my mom told me a friend of hers told her,when her boys would fight, she would tie them together, and they would have to go all day long being tied together and what one did the other had to do as well, or go as well, and it tooks a few hrous and finally they got so tired of being with eachother attached at the waist they were kind to one another, and well I did this and it was funny but at the same time it taught them, that fighting was not worth it, and they have since gotten along alot better, now when one goes off to a friends house, the other gets somewhat bored and misses his brother, they still have their days, but it's not as often as it use to be.
so you can try that, and see how it works, other than that, try to separate them for a while and se how things work out, I have had to do this as well. they get along better now than they use to. so hope this helps.
D.*Ü*