Woah, in all this Totland mess I somehow forgot that "Bonney being one of BM's daughters" possibility was a thing.
Not sure where to stand on it now. I guess it's still possible. Normally, you'd expect one of the members of Charlotte family or BM herself would mention her. BM was complaining about Lola, shouldn't she mention Bonney as well? Of course, it wouldn't be the first time Oda withheld information like that.
But I must admit, not convinced as I was before.
Bonney and BM can likely manipulate their age. I think it's also possible they're sisters, but Bonney has been low-key for a long time.