Words, Words, Words, Words

I see why you're concerned about the girls, but I think I'd reserve judgment until I saw more of how the grandmother cared for them. I do think that in many cases violent adults are the products of abusive childhoods, but I don't think it's always that way, and when it is, it isn't always the fault of the family. A kid who was sexually (or physically, though that's less common outside of the family) abused by an uncle, a family friend, a priest, a teacher, or a stranger may have been troubled and acting out for years, eventually turning violent, without its having anything to do with his family. He could have been a victim of some horrible crime that turned him hard and then violent. In addition, violence sometimes just comes from out of nowhere. Sociopathy is something even the most loving family can't prevent or cure. Of course, sociopathy's rare. Addiction, as you mention, as well - that can be entirely genetic (sometimes), nothing to do with nurture, and still lead people to do some really awful things.

I'd say that while you have cause to be concerned, I wouldn't make any judgments just yet. I'm really glad you're so concerned for them, though. I don't know whether you'll see them again, but it means a lot just to know that you care.