I remember potty training seeming like a much bigger deal before we tried it than the reality ever was. Someone suggested I buy one of those handheld carpet shampoo thingies, and it did get used! Only a few times for pee though. I have heard that boys are harder to potty train and honestly I think I've heard more horror stories from parents of boys but I have known a few girls who resisted.
We bribed with candy.
Aw, bap. That sounds really hard. But it does NOT sound like paranoid (or any other kind of) schizophrenia. Anyway, schizophrenia doesn't usually manifest till at least the late teens, so you have a few years before you have to worry about that.
I don't know if you've gone for a psych evaluation but IIRC (grad school was so long ago now!), mostly they don't diagnose children until age six or later. The personality and development are too fluid and too rapidly developing before then to make a positive dx.
But that doesn't mean you can't get help or support. Have you had any help or support (if you don't mind my asking)? Have you read The Highly Sensitive Child? Am I irritating you with unsolicited advice? ;P
The power of Peer pressure. The boys were more interested in going potty when in child care or spending the day with their cousins (the same age and potty training at the same time). That could be why he's doing it at school.
With all the changes at home perhaps this is the one thing that he feels he has control. At least that's what I've seen with my boys and their reactions to periods of transition.