I am so sorry for your loss. I am glad you are in recovery. I lost a child 23 years ago...and in the course of working through that loss, I learned about suicide...and it is a very tragic act...but also an act of anger. I cannot tell you more than that, but it made me think and as I have lived through more things in life...and awakened to the fact that I had an alcoholic Dad (who was loving regardless) and an alcoholic mom who is narcissistic and in denial and has scapegoated me...and other things, I remind myself that I am living and enjoying so much more about life than I did even 10 years ago.
You did what you needed to do to take care of yourself and am very happy that you continue to do so. I like the suggestions above...I know you love your sister and your nephew. You may be surprised at how well your BIL might find a way to take care of himself or be taken care of.
I like the suggestion about seeing if you can talk your BIL into getting counseling for your eleven year old nephew...it is critical for his life possibilities even though we can't plan on outcomes. I did that for my own kids and family when my son died...and myself and it helped me tremendously and through many more hard times...including one now.
Hang in there and you are strong. Suicide is meant to incite guilt in others...although, like so many diseases...including the depression and anxety I have...it is not always conscious.
You are in the same place I am...different circumstances...I am having to 'let go, let God' of an active heroin daughter. Just continue working your program and know that God is handling all. I didn't know when I signed on today that I could say that...but when I say something that I truly believe in...I know that I need to do it to.
Gentle huggs.