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Ok thanks anyway Lan, i have since done a bit of research on this question and found this answer that may be useful to anyone else wondering the same thing............
Hi,
Really it will be no different with these being brothers. Although the fighting may start later than sooner, they more than likely will still fight. It is not just a dominance issue we are looking at, it is also territorial. They can be kept together for a little while, until they are about 4 months old, then they will be sexually mature, or getting near it, and they will start fighting. most bucks also spray urine to make their territory, and with them being together, they will spray each other. They would be really hard to keep clean. So your friend can keep them together for probably just long enough for them to get another cage for one of the bucks.