Are the brothers neutered? You won’t be able to bond them otherwise. If they are, it may be that they will never be able to be together if your bonding attempts haven’t worked so far. You didn’t say how long you how tried bonding, maybe they can be together and be bonded with further attempts. Rabbits can also hold a grudge, so the fact that one bit the other’s ear might make future bonding harder.
It would be best to keep the new bunny separate from your other two, until he has been neutered and a month has elapsed. I have never had a trio, so I’m not sure if it would be better to go ahead now and try again to bond your two, or to wait until the new bunny has been neutered and try to bond a trio. Sometimes, a new bunny coming into the house can cause upset and even bonded rabbits can have problems with each other. If you aren’t able to get the brothers bonded, the 3 rabbits may have to always live separately.