Like elephants are said to - Basenjis never forget.
Once they fall out, they remember and they bear grudges.
it CAN be done to bring them back in harmony - I have done it myself. But it is a long, slow, process.
Spaying either will not make a hap'orth of difference. You may just have to live with two teams. I've had to do that too. The boys were happy in either team but the three girls were rabid - 1 against 2. So either one or two bitches was(were) crated at all times while the other(s) stayed free with the boys. Teams were swapped every couple of hours throughout the day and took it in turns to be free at night.
Eventually the 17 year old girl died and I was back to one team again !
But I would not have spayed any of them - a totally useless exercise in these circumstances.