I can't really answer your questions about your rescue situation....although I wish I could! There's lots more experienced folks that will be able to help, though.
My concern is with all the other animals in that apartment. It sounds HORRID! Have you considered calling the ASPCA and filing a report? If they can't afford to feed ONE boa...how the heck are they feeding all the other animals they have? And having a room full of "pet" rats while allowing your snakes to starve to death because you can't "afford rats"????I'd definitely be calling SOMEbody and hope to get that apartment cleaned out of ALL animals. The poor beasts!