My heart goes out to you, I know you are hurting, wish I could say some magic words that would help. Will be praying that the boys are kept safe. Like the others have said call CPS so they will check on them, also if she would have your Mother call them with 2 of you telling them maybe they'd be more apt to do something, don't know but it's worth a shot. Were they reported before ?
Again I'm so sorry for you an the kids that this has happened. It pisses me of the way some of these so called Mothers act, they don't take care of their kids, choose drugs an boyfriends over the kids. Then cry an carry on about how someone tried to stop them from taking them. My daughter is the same way with her son an it makes me sick. If they think their damn drugs are so important then why not at least let the kids be with people that love them an take care of them. Sorry it's just a sore subject for me.
Stay strong !!