I have a sibling pair of Grt Pyr mix but mostly GP, male & female. They are 10 months old. The male has always been very mellow but is beginning to show aggression towards my other dogs (his sister and a Pitt Mix they have been around since they were small). I discipline him and he gets it but then slowly slips back into biting them when they come close to me - not a dangerous growling bite but a quiet slow bite and his body language definitely changes.

My male is not neutered because I was told to wait as long as possible so his joints and bones would develop correctly to avoid health issues for him later that are common for the LGB (hyp dys, etc.). However, I have just scheduled him to be neutered in a few weeks because he suddenly became extremely aggressive with the Pitt who walked up to be petted by me when my Gr Pyr male was right by me playing a very rowdy game of King of the porch. It turned bad quickly as the Pitt did show some snarling and the puppy lost his temper. He did not try to kill the Pitt but he could have very easily by accident.

My Gy Pyr will lay down and show me his belly when I am angry with him, even just a loud No can do it so he does not seem to feel dominant to me. What is the best way to train out this behavior of not allowing the other dogs near me without jealousy? I give him tons of attention and make sure to not break my contact with him if others walk up for a pet as well, rather I pet them both and use soothing words and encouragement to teach him it is not an all/none for my attention. Not sure what to do next.

Thank you!