First, and very important, the path your brothers have chosen is not, not, not your fault. Like many people who are troubled, your brothers cast about for someone to blame rather than take responsibility for their own choices. No one is “making” them be addicts. If they want to get sober, there are programs that can help them. Blaming doesn’t do a thing.
At least some of your distress may be because you aren’t getting enough regular, restorative sleep. Sleeplessness contributes to anxiety which contributes to not being able to sleep. You need help breaking that cycle. Please see about getting some coaching or do some reading about how to establish better sleep.
As for your concerns about working with children: I can’t think of anyone better. You know personally what it feels like to be abused, blamed, and upset as a child. My guess is that you are acutely sensitive to when one of the children in your charge is distressed. Once you get a better handle on how to deal with the echoes of your own experience, you will be in a unique position to be helpful to them.
That being said: Therapy often happens in “chapters.” You had some play therapy as a child that may have helped you deal with the immediate situation. Now that you are older, you are rethinking those events from the perspective of an adult. I suggest it’s time for another chapter of therapeutic work. You are spinning with self-blame and anxiety. A therapist can help you find a way to come to terms with what happened and move on. Do make an appointment soon. You deserve to have a happy adult life.
I wish you well.