She's obviously in an abusive situation (as are her animals), and this may very well be her first attempt to reach out to someone for help. Good for her, but you are under no obligation whatsoever to fix her and her problems.
You need to get out of there as quickly as possible if you have not already. Just leave. This is your own personal safety we are talking about. There is no wiggle room. Period.
As for what to do, you could potentially be doing an enormous favor (or not, perhaps) by calling the cops on your way out the door. Will he take it out on her? Possibly, but at least the authorities will be in on it. Call Animal Control as well. The dogs and cats don't deserve to live that way, either.
You cannot fix her, but she is a grown woman, even if damaged. The animals, however, are in no position to ever help themselves. Plus your neighbors are innocent in all of this.
But get a new place first. Make it a priority - do it yesterday. You do not have to be a part of this.