I'm thinking of disbanding my prom group a week and a half before prom
Why did you wait so long?
Celebrating prom with them is like celebrating as a family and I hate my family.
I think that it is too late to cancel now! It could ruin the entire thing if you cancel right now. You should have thought about this sooner.
I can cancel it if I want to and I will.
You are making decisions about the prom for the whole group and that is not the way to handle it. Set aside your personal preferences and let the group decide or you will ruin their night.