I can imagine what you're going through. I went through it with a sister 10 years younger than me. I left home at 17 desperate to get out of it. My sister NEVER forgave me for leaving. This was 35 years ago!
If there's any way you can get the kids on the weekends to get them out of that mess for a rest from it, it would help them.
Also, if there's no food, there are food banks everywhere. Never give an addict money. Give them food or cloths you purchase.
I am so sorry you have to go through this. I know how heartbreaking it is.
Keep coming back and posting. It helps and it enlightens.