Your family only shares part of your genome. Even if you have full sequence data on both parents, you don't have anything near full information about the child. With siblings you would have less information, and the information gained from distant relatives becomes astonishingly small the farther you go. Don't assume that your DNA is fully compromised just because someone in your family has surrendered it.

I work to apply encryption directly to DNA molecules, the Fort Knox of DNA data security ;)