Board Thread:Speculation House/@comment-25574297-20141024020130/@comment-6863431-20141108004738

To add to that, Monty's reply to a headcanon someone had about Cinder being Blake's mom was something along the lines of "Yeah, no, Cinder isn't Blake's mom." Kinda shoots that idea down.

Also, Cinder's human and Blake's a full Faunus. So sadly they can't be related by blood.