What relation is your grandfather's second wife's child to you?

Answer 1

Assuming you are descended from your grandfather's first wife, or his third, the child of your grandfather with his second wife is a half-sibling (half brother or half sister) you your parent. Thus, the child is your aunt or uncle. (Some would say your half-aunt or half-uncle, but such terms are not widely accepted in genealogy.)

If the second wife's child is not the child of your grandfather, but your grandfather adopted the child, that child si step-brother or step-sister to your parent and your aunt or uncle (Some would say step-aunt or step-uncle, but that term is not widely accepted in genealogy.)

If the child is not your grandfather's biological child and you grandfather did not adopt the child, then the child is not related to you. However, if the child was young when your grandfather married his second wife, everyone may have treated the child as a child of your grandfather, anyway, and you can too.

Answer 2

If your granddad's second wife is also you grandmother, you are first cousins. Otherwise, you are not related at all.

Answer 3

your first cousin if you claim your grandfathers wife your grandmother .