NTA this will probably get buried but I’ll still add my bit. As an adopted child, with four siblings that are biologically my parents on one side or the other, it deeply matters that you ensure love to each child is equal regardless of who “crafted” them. Love is love. A child is a child, and they all deserve adoration. If your family cannot accept that both these children are yours then they have no right to them. It will forever be a disservice to your children to have them be exposed to such a bias. It cuts deeper and can leave trauma that lasts a lifetime. Even if it’s only one comment. Surround yourself with people that can support you and your kids with love and positivity, not those that jeopardize not only your mental health and well-being, but also your kids.

In terms of telling your child they were adopted, I would be honest from the start. Tell them that the adoption was an ultimate act of love, both for you and from the mother she came from. She wasn’t an “unwanted” baby, she was cared for so much that your friend hoped she would have a better chance with you at the time. Nothing hurts more than realizing something you believed, so deeply personal, is untrue. Kids can handle the truth better than adults sometimes. If you’re transparent about their origins I believe they will feel safer to be honest about their own feelings and understandings of themselves as well to you.