What about watching him "parent" this child? What if they did things in a way you disagree with? How will you manage watching that?

When I think about whether I could accept eggs from my sister or if I would donate eggs I was always anxious of what she might perceive of my parenting and whether or not she agreed with the way I parented, I would always worry and be over anxious of that.... I always thought that it would be so much harder if it was a family member as it can be harder with family due to the history of the relationship....

You guys might be fine, but just something to think about... Your relationship with this child is different to other nieces and nephews.... It always will be, and it does not end the moment you hand the child over. It's there for the rest of your life.. Its a special relationship, but if could be difficult as well... can you live with that???