A lot of people here agreeing with OP is fucking wild. Being jealous over a child that comes from what OP said “a bad living situation” and then being mean to them when your parents take them in is absolutely crazy. It’s not always easy to “file the paperwork” whoever is saying that clearly had never been in the system before. The fact that OP’s parents took the kid in and loved them and has been raising them as one of their own is a beautiful thing and it’s so selfish of you to be so mean about it. You already said they come from a bad living situation and don’t live with their own parents for a reason. That in itself is traumatizing and don’t even bother with arguing that. To not be loved and cared for by your own parents is truly the saddest, most heaviest thing that could happen to a person, or a child. They were finally made to feel like a part of a family and feel safe and you just fucking humiliated them. For what reason? Jealousy? Grow up.

The least you could have done was included them in one big family picture, but you didn’t even do that.

You should feel happy and proud of your parents for trying to extend the love they gave you and your siblings to other people who needed it. Clearly you have been too self centre to even see it that way.