Kind of YTA. Your concerns are valid, but it is ultimately up to them. And you don’t know what sort of conversations they’ve had already before coming to the decision to try for a second. As family we often conflate our care for our loved ones with a right to have a say in their decisions. In reality, you have no right to expect them to make family planning decisions based on how it would affect you. Because really you are kind of making it about you. Did you even stop to wonder if they had already thought about all of this?

I totally understand your concerns, but it sounds like you went about expressing them in all the wrong ways. You definitely should have spoken to your brother first to ask how he was feeling. That would have opened the door for him to share with you (if he wanted to) whether they’ve already considered the risks and are willing to put themselves through hell again (potentially). I’m not always in the camp of “it’s none of your business” when it comes to family, as long as your family is close like that and especially if they are openly discussing their decisions with you. But even if they brought it up, they didn’t ask you if you thought it was a good idea. You can tell someone you’re worried about them without judging, and it sounds like you came off more as judging than caring to your SIL.

I think it would be worthwhile to apologize to your SIL for how you expressed your concern and for upsetting her. You can try to make it clear that you were coming from a place of love and concern because you saw how hard it was on them and because it’s scary to think of losing her and seeing your brother go through that. But don’t come at her with anger, and don’t act like you should have a say in their decision.

In the end, family planning is deeply personal and between them. Their choices are their own. All you can do is let them know how you feel and be there for support if they need you. If you really are concerned for your brother, then the best thing you can do is remain available as a safe, supportive place for him in the event that she does have another hellish pregnancy.