I don't know that there is much except you were able to see the truth in that family.I'm trying to find the good in the situation
I am not certain how old you are, but you sound young-ish. That was a horrifying situation for anyone, let alone someone who is young. As we age, we start to 'see' stuff. A quick story.
I had a friend in school. Her father used to creep me right out every time I ran across him but I had no idea why. In grade 7, in the middle of the night, he woke all 5 of his girls and their mother up and shot himself in front of them by the pool in the back yard. And I got to thinking. I was in that house a ton. I didn't realize what went on in that family.
And then I got to thinking some more. Why didn't I see that? I thought about some of the things my friend had told me when I was younger and thought 'why didn't I help her?' Because I didn't get it. And if I didn't get that, what else wasn't I seeing? It takes age and experience to see stuff and even then some families hide this stuff so well.
The good is that you have now seen it. That family is messed. Danger. Stay away. You were not the responsible adult there. I feel like you have catapulted yourself into taking on something that was just way too big for you. It was the parent's of your friend who should be assigned responsibility for this - not you.
Be well. Keep safe. Much peace