We are a blended family but he treats his kids completely different then mine

We have been together 6 years he has 4 kids and I have 1 (no kids between the two of us) all the kids except the oldest live with us since we moved into a house in May (this is our second time living together, we split for a little while and I lived in my own for 2 years after living together for 2) we discussed schools before moving the 2 oldest will stay at the school they are at due to about to graduate and the other in special classes and the 2 youngest will move to the new district near home. Now 2 weeks before school starts all of a sudden he tells me his youngest does not want to move schools so my bf has made all kinds of arrangements for him (when arrangements would not have been needed before bcuz the school is right across the street from our house) so he can go to the school that he wants and pretty much just told me as a FYI. Now I don’t think it’s fair my daughter who is going into 7th grade has to move to a complete new school where she knows absolutely no one but his who is going to 5th gets to choose. I told him how I felt and it turned into a argument and it feels he’s not even considering how my daughter is feeling. I’m so hurt bcuz my daughter has cried to me that she’s so scared about this new school year and she’s gonna feel like even worse bcuz his kids get to choose where they are going. Please help I need advice how to address this with out it being such a huge argument and how to show him it’s suppose to be equal with our kids