If Helena Ravenclaw is Rowena Ravenclaw’s daughter do you think the other ghosts are relatives of other founders?

Every pureblood is related in some way, so probably- but if we're talking about closely related, I'm not sure

It's possible, though not necessary

No I think that was a coincidence. The other house ghosts are just people from that house

No but It can maybe (maybe I will add it in my world of Harry Potter)

Probably not.