Changing name after adoption

My husband and I have been foster parents to my nephew for 6 months and we are wanting to adopt him. My brother and his girlfriend have done nothing that they are supposed to do for reunification. They still say they want him back, but they don't want to do anything that DFCS tells them they are supposed to do (drug assessments, mental assessments, rehab, paternity test, etc.) They absolutely refuse to cooperate with anyone, so the case manager will be filing for TPR next month. Anyway, all that to say, my nephew has his dad's name as his middle name and we are really wanting to change his middle name (we are keeping his first name and changing his last name to our last name.) My concern is that later when my nephew is older, would he be upset with us for changing his name from his birth father's name? My brother is one of these types that plays the victim VERY well and is very convincing. I'm afraid that he will try to turn my nephew against us by blaming everything on us (he already is telling family members that we are stealing his son) and I don't want anything else that he could fuel the fire with. Maybe I'm just making a bigger deal out of this than it is, but I just really don't want his name to have any connection with my brother.BTW, my nephew is 18 months old right now; he does not know his middle or last name yet.