We see a lot of the girls trying to impress Katakuri and they get embarrassed when he looks at them and their hearts will race if they think he is going to praise them.
I don't think this is normal if they look at him only as a brother. Maybe I'm wrong to think that way (I'm an only child, not much experience with siblings) but was there ever any indication that a romantic relationship is possible between siblings in the Big Mom family?
Was there ever any indication of siblings getting married in the Big Mom family?