Your parents' father andmother.

Your parents' father and mother
直译:你父母的父亲和母亲(也就是你的爷爷奶奶)

你的祖父祖母

?? What do you mean? I could not really understand. Please ask a little clearer!
one's parent's father and mother are one's grandpa and grandma, or grandfather and grandmother.

祖父母或者外祖父母

你父母亲的父亲及母亲? 你想问那一个?

Your father's father & mother is called grandfather & grandmother.
你父亲的父亲和母亲叫祖父及祖母

Your mother's father & mother is called grandfather-in-law & grandmother-in-law.
你母亲的父亲及母亲叫外祖父及外祖母

你父母的父母亲（也就是祖父母）