I will tell you about our last two experiences. I was laid off from my job in 2016. Moved from Cobb Cty to a smaller town in Georgia. We put our son in private school and we were set. He had met the new baseball coach and they seemed to hit it off well. He was an 8th grader and when the season began well the fun began. Parents did not want much to do with us. We were not part of the private school group that went their from kindergarten on up. Had to deal with the kids not wanting to have anything to do with him - just as your son. When he moved up to 9th grade some parents did not like the coach so they got him fired and replaced. Well my son went down on the food chain. Kids he played with the year before got a jersey - mine did not.
Did not matter since I was offered a new position I could not turn down in the town I grew up in. Well the same thing happened. Liked the coach as a 10th grader and then bam a new coach was hired. New coach has a lot of talent sitting the bench - not even including my son. But the same situation with the parents - ignored by almost all. It was strange - my dad would come to the game and he would see friends from when he played for the same school in the 50's. But the parents were still standoffish. I started to see that when you watch them - they tend to break up into the same groups they had in little league. Since my son did not play little league and did not play around here then it is hard for him to be accepted. Believe me a lot of what you describe is the same that happens to my son. I just tell him to put his head down and do his job when given the chance. He has done that quite well when given the chance - and some of the kids and parents have started to talk to us - not many - but it is a start.
The thing is other kids he knows in the school have the same issues as he does. One of his friends had been in the school for about 2 months when my son started. He too was a transfer. My son was the first to have spoken to him and this school has one of the largest military base in the country near it. You would think they would be used to transfers in - but I guess not.
Good luck on whatever you choose.