Is it unreasonable to ask one of my fiance’s daughters to be bridesmaid because one is biologically his and the other isn’t?

My fiance and I are starting to plan our wedding and he’s now upset because I only want one of his daughter’s to be a bridesmaid. I’m closer with one than I am the other. Of his two daughters, one is biologically his, the other isn’t. The one I want to ask is biologically his. The elder isn’t his, but he’s known... show more My fiance and I are starting to plan our wedding and he’s now upset because I only want one of his daughter’s to be a bridesmaid. I’m closer with one than I am the other.
Of his two daughters, one is biologically his, the other isn’t. The one I want to ask is biologically his. The elder isn’t his, but he’s known since his ex told him that she was pregnant, as he’d been out of the country weeks when she discovered she was pregnant. He fell in love with his eldest the moment he heard her heartbeat and didn’t care that he wasn’t her father. She however isn’t aware. They have never told her, as they don’t feel like they have to. Oddly enough, her mother is now married to her actual biological father.

My fiance is really mad that I want to only ask one of the girls, even though I’m only close to one. The elder one and I don’t get along, she’s incredibly close to my fiance and doesn’t like anyone else getting close to him. I’ve tried but we don’t have anything in common. He’s arguing that I’m choosing his biological child over his nonbiological child which I suppose part of me is in a way. I did make more of an effort with the younger one, as I went out of my way to try and make a connection with her.
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