My child's cousin might be moving to his school...

My son " Harry" and nephew "Jim" are both 6 years old. We live about 15 minutes drive from them and see them every few weeks. Harry and Jim get along really well but they are very very different. Harry is very sensitive, prefers to play with the girls, is very academic but can also be very silly and loud. Jim is much more of a typical boy's boy- he plays with the boys and wants to spend all his time playing soccer and Star Wars games.

The one thing in their dynamic that is problematic is that Jim is very competitive, and Harry is a real follower. Jim is always asking Harry if he can do this or do that, comparing what they know or what they watch or what they are good at- and Harry always wants to do whatever Jim does. They attended preschool together and this dynamic wasn't so great. Jim had a little gang of boys and they would run around playing soccer, and Harry really really wanted to fit in. He'd try and play too, but Jim would say that Harry wasn't very good at soccer and Harry would feel sad and left out. The thing is, he doesn't even want to play soccer- he just wants to play with Jim. I was secretly happy that they were going to attend different elementary schools because Harry could find his own people and be his own person, instead of trying to keep up with Jim.

The problem is they're about to go into their second year of school, and now my brother (Jim's dad) has announced that they're going to move Jim's schools so that he can go to school with Harry. Secretly I am a bit devastated about this. I just have a strong feeling that Harry, who has absolutely thrived at school so far, will once again only want to play with Jim instead of the nice kids he's befriended so far- he will act silly in class to impress Jim and not progress as much academically as he could. I think that Jim will be competitive about friendships and skills and Harry will want to keep up with him in various ways. It could be a good learning opportunity for Harry to not try and be like someone else and learn to be his own person with his own skills, but at age 6 it's hard emotionally to do that. I also wonder about the boys misbehaving in class, or getting upset about one getting invited to a party that the other wasn't and things like that. I have REALLY liked having them at different schools and I don't know if I should say anything to my brother before they make the switch. I think this has all gone totally over my brother's head and he just sees how much the cousins love each other and wants to them to be best buddies at school too. As well as this there are other practical reasons why my brother wants to move Jim's schools and it's not really my place to ask him not to make that change if it's what suits them.

Any advice about how I can approach this??