I've only sold one gun to a family member, my older son, at below market value. Don't feel bad for him, I gifted him a Les Baer 1911 as a welcome home gift from his first deployment in 2006. At some point he'll also end up with whatever I have at the time I don't care anymore.
Price depends on the family relationship. I don't have any other family members that share our firearms interest.
I had an arrangement with a late forum member, IBSandy who passed in 2012. If either of us bought anything from the other we got a good price and also the first right of refusal at the same price if we wanted to sell. I made the same arrangement with a current member, that's how I roll.