Well it sounds like you’re already doing all you can for your son, I guess it’s more about getting the other adults to behave like adults! I know how complicated that can be, all I would say is continue being the reasonable one and keep at the angle of what’s best for your son when challenging them as diplomatically as you can. Don’t know what else to say but I’ve been there and am thankful that all the adults here are putting kids before their own feelings, it’s taken some time!