Should I pick the people I'm being told I should have as bridesmaids?

I am estranged from my family and don't have any close friends as I moved A LOT when I was younger. My Fiance has a large extended family and they're all amazing but I've always said I don't want any bridesmaids as I don't want to have people "for the sake" of having them or because it's what others expect me to do. My Fiance and his family have made it clear they expect me to have his sister and his cousin. But, I don't want them. What do I do? How can I disappoint that many people? Advice?