The thought that sticks out for me is just to let them know that they can call you 24/7/365 if they are ever in any danger, scared, afraid, or just need a friend they can trust that has their very best interests at heart. Let them know you will go to any lengths to help ensure their safety and that they can call you anytime, day or night...they can even text a simple code word to let you know they are in danger. Make sure they know how to take care of themselves in an emergency, how and when to call the police if necessary, give them phone numbers of neighbors and other relatives, and perhaps the number for Alateen or other crisis hotline. Ask neighbors and teachers to keep an eye out and to alert you if they think there is a problem. Check in with them regularly.
Just my $0.02. It's a dreadful situation and I"m sorry you are in it. I hope we can help to support you.