Loving dog turning against his house mates. Please help?

My 11month old fixed male pit bull was neutered a month ago.We also own a 4 yr old female pit bull who is spayed. We recently moved to a larger home with a fenced in yard for our dogs. We lived in a small apartment and needed more space for the pups. Our dogs are food aggressive and we rotate their schedules to avoid confrontation. In the past they have fought over food but it was rare and almost always our fault. since our male has been neutered though he has developed a severe amount of aggression towards our female pit bull and our 15 yr old boxer. He has grown up with both these dogs. Here's the catch. In our yard all three of them will play lovingly and lie together in the sun affectionately. The moment the dogs come inside the pit bulls attack each other. not several minutes after entering but as soon as they cross the threshold. Our female is fine with our boxer but our male has inside aggression with him as well. When neither dog is around he is a well trained loving animal and can still play with other dogs at the dog park or friends. I've started to crate and rotate to avoid injury. i still don't understand what is going on. I'm afraid I'll have to get rid of our male but hate to get rid of him with his breed. He needs consistent training and I just can't let him go. I've even considered moving into my own apartment with him and living separately from my gf and our other animals. Please help. any suggestions would be great. Please understand that i am educated on his breed and am not an irresponsible pit bull owner.