So, this is frightening for you and them too. My deepest sympathies for everyone. I don't have much advice to offer, only this. If part of your worry is financial and you are in the US... I believe that a court will actually need to assign you as custodial guardian of these kids. This will help them immeasurably for college, health care, etc once they're in your care and in their future.

IANAL so consult with one (I assume you already have of course, but if not, do it). I gained custody of a nibling when he was 13 and had he been more focused on college and less on girls and trucks, his college would have been free and then some.

Good luck and condolences.