Boar trios are notoriously tricky. Only in exceptional cases will they work. Personally, I wouldn't advise it at all as it could disrupt the relationship between the current pair. They have also yet to reach their adolescent phase. When they do so one of the younger boys may challenge the older boar for authority - this could potentially lead to a serious fall out.
Has your friend considered boar-dating the older boar, so that he might find another friend of his own?