knt013

I'm glad you've found us. Has your SIL been diagnosed with BPD? People with BPD have a major fear of abandonment. My guess it that your relationship with your brother triggers that fear in your SIL... .she simply can't share him and I wouldn't be surprised if that wasn't behind some of your estrangement... .Your brother trying to make her feel secure.
What I see is a sister who loves her brother and his kids. You are absolutely doing the right thing in supporting him. SIL's marriage sounds like it is falling apart on it's own and she is just trying to blame you for her issues.
I'm so sorry for your brother's loss but it does sound like it has been a catalyst for him to face and deal with the problems in his marriage. Your brother is also doing the right thing getting help himself and that will also be beneficial to his other children. It sounds like he is coming out of the FOG (Fear, Obligation & Guilt - emotional blackmail) regarding his wife which is also a healthy thing.
I want again to validate your support of your brother and his children. Just keep doing what you are doing... .keep supporting him.
You might want to refer your brother here too. It's a great place to find support, get information, and learn more about BPD.
I come at BPD from a different angle, I'm dating a man with an uBPDxw (un-diagnosed BPD ex-wife) and we both come here for support, and now we speak a common language and have a common strategy when dealing with the ex.
Again Welcome
Panda