Sounds rough. My first thought is you guys need to seek some professional help. You mentioned that she takes anti-depressants, is it possible that she is having bad reactions to some medication or maybe the medication has been masking a bigger issue, etc? Just my first gut instinct based on what you wrote here.
I would recommend that you also speak with an attorney and see what's necessary to protect yourself and your kids (or your access to your kids), even if you guys decide to do nothing, it doesn't hurt to be informed.