Nope. Never have and never will. The only way I would suck off a member of my family is if I didn't know I was related to them. If I am blood related no way would I ever.
The closest I ever came to anything like that was with my step-sister. Her father married my mother. When they met we were both teens.
So we weren't raised together. Actually my mother moved out of state when she got married, so I didn't meet my step-sister for sometime after they were married.
So when I went for a visit one year we first met and I never thought of her as my step-sister, thought of her as a friend (still feel that way I guess its because I have only seen her twice in 9-years).
But when we first met there might be some touching, but we never did the deed. She's hot to LOL. But even though we aren't blood related it wasn't right. I don't wanna screw up my mothers marrige.
So blood related or not I wouldn't do it. One cause blood relation yuck. And by marrige could cause problems so I never would.