Fuckin' christ. And I remember now, he sounds VERY ill. 
So now she's getting stuff in writing, hopefully overseen by a lawyer, to make things like kid visitation contingent on a psych evaluation. She also told him she may stay if he sees a doc. He countered it should be marriage counseling. However they have tried that. He went along with it during sessions, and then did fuck all after.
Also, semi-related to this bullshit, his mother is a jerk. I know very few people that give off insta-jerk vibes, but she's one. She also thinks she's helping by going shopping for things for their house to surprise them, and then sending them a bill. This included a new couch and a new tv. Also she got shit-faced at a baby shower. Who does that? She's also in the medical field, just many wtfs.
https://www.nimh.nih.gov/news/science-news/2013/five-major-mental-disorders-share-genetic-roots.shtmlNot only am I quite sure that your brother-in-law has Schizophrenia, or some variant, I would venture to guess that the mom has Bipolar symptoms that may not have been addressed. Making large, surprise purchases for people and then sending them the bill during a stressful time implies severely lacking Cognitive Empathy, which is common in Bipolar Disorder and related disorders. And considering the similarities in genetic predispositions to both Bipolar Disorder and Schizophrenia, it would increase the likelihood of either one having a disorder if the other were to be diagnosed.
Obviously this is just conjecture, but the blunt presentation of your brother-in-law's symptoms coupled with the
very bizarre nature of his mother's behavior (Seriously, I've never even heard of someone doing that. Who the fuck does that?) makes it something worth looking into, IMO. Maybe evidence of a pre-existing condition in his mother, and proof of the similar genetic roots could convince him to do something about it? I wouldn't think so, but every argument counts in dire situations like that. Marriage is a pretty big deal.