It’s not super clear, since I think turning to stone had more to do with removing your emotions, and the hair turning white seemed more to do with being disconnected from her selkie self.

Perhaps, it isn’t made super clear. My interpretation is that they are simply animals of the natural world drawn to the selkies and their family since they see them as one of their own.

It seems as though Bronagh only passed on her selkie-ness to her daughter and not her son, meaning Ben is a human child born to a selkie mother.