Comment by owaislone

> are they sharing Google accounts, photo albums, or were the photos shared in the same whatsapp group?

None of these. They don't share any accounts. I don't share any account with my father either. Me and my wife use the shared galley feature. The photos that ended up on my fathers phone were shared by me and my wife with each other on whatsapp. I suspect either mine or my wife's gallery somehow "leaked" into my fathers even though none of the accounts have any connections AFAICT. Probably we clicked some share button somewhere accidentally but I couldn't find any shared galleries on any of our phones.