I have 4 adult dogs. One male was neutered and our female has attacked him. I am concerned about our other male. What should I do to stop this fighting?

I have three German Shepherds - a 4 year old male, a 4 year old bitch and their 18 month old son. My bitch and dog got along great and mated. They had 9 pups and we kept 1 dog, now 18 months old. But the bitch was a rescue dog who was previously mistreated. We had the dog castrated first and at a later date the bitch spayed as she shows aggression to anyone but myself and my husband and 3 children, but found this was a big mistake getting the dog castrated because since then the bitch will attack and if she got the chance, kill the dog even though he is double her size. I am aware the problem is we have altered the packing order having the dog neutered - he is now an outcast and no longer top dog. Spaying the bitch didn't help either, but aware of the problem we keep the dog and bitch separate at all times except when accidents happen and I only wish I had visited your site before they had their recent encounter. The bitch managed to get the dog on the back of the neck and clamped her jaws fast. I physically pried her jaws apart letting the dog escape but not before he had nipped me leaving large bruises on my arm and she clamped her jaws on my finger. Each dog didn't know they had hurt me and didn't intentionally bite me. The problem is I would like to have the 18 month old dog castrated but I don?t want the same thing to happen. I am worried the bitch may turn on her son if I have him neutered. Could you please advise me?

Monica