Wow, that IS huge!! And places quite a load on you!!
First, and Always, devote it to prayer!!
Your sister has been given information about God, we can’t mess with free will!! She has to be “let go” in a sense. No help, so she can be forced to a better life. If we keep helping those who continue to hurt themselves and others around them, then we do not love them!! TOUGH LOVE, it is necessary sometimes, and is much harder on us than on them!! But if she is never faced with “no where to go” and I do mean Literally, then how can she be faced with Devine Intervention?? Sometimes, we have to let our loved ones fall so hard that they hit face first into concrete, so that They will call out out to God!! Because they will have on one else to call on!! We want this!!
Your obligation at this point is to let God save your sister and you must save those kids!! They are the innocent ones here. If you know abuse or neglect or endangerment is occuring it is our Godly and Civil Duty to protect the children at all costs. Do not Delay another moment!! Child Protective Services have a hotline, you can call anytime.
If you do not want them involved, threaten your sister w/ them. Let her know you are leaving and you ARE taking the kids!! She WILL fight, but just let her know, there is nothing else you can do for her except the biggest favor, making sure she does not kill her own kids!!! So, you ARE taking them or CPS is taking them. Those are her ONLY choices. and leave her NO money when you leave. Why feel obligated to give HER money when you are taking on even more financial responsibilities of hers, her kids!!
my prayers are with you. This is more serious than you could know.
My own experience: I suspected my friend of doing drugs and feared for her child. Then all the physical signs pointed I was right, and then came other things and so forth. I hesitated and her 13 month old ended up in the ER in cardiac arrest, they found cocain in his system!! Talk about GUILT