His pond is less than an acre, so unless he can separate the pond for the various pairs, he is only going to be able to have 1-2 pairs realistically. If you are already having problems with the swans which know each other, there is nothing to say that they will or will not get along once placed on his pond.

Additionally, the current pair he now has, more than likely have established his pond as their territory and may or may not accept any new swans. Again, he may need to separate the pond so that two pair can reside without any fights, chasing or other defensive behavior. But, we would not suggest placing more than 1-2 pairs of swans on a small pond this size. If fights occur, he will need to find a good, safe adequate home for the two introduced swans. The Regal Swan