When we were having trouble ttc, my sil and I were driving somewhere when she said, out of the blue, "you know if you can't have a baby, I'll have one for you" I was overwhelmed! Knowing how amazing it is to be a parent, if one of my brothers wives could not carry a baby I would seriously consider it for them. Using their embryo would be my preference though. I don't think I could do it for a stranger or even just a friend though.