Christmas must be interesting.
His kids have two sisters? Half?
Twin sisters?
It's a riddle but I get it! Robert Planet has three daughters in total... ... Or two girls and an undetermined number of boys!
Pick up your prize at the front desk!
I’ve solved it. He has been married twice and has children from both marriages. His second marriage was to the sister of his first wife.
His first wife was an East Indian woman, if I recall. I think "That's the Way" from Led Zeppelin III was inspired by their relationship.