I agree with MDP and sciski. Even if he is an SJ of some kind, that's not why he's acting that way. He's got issues to the point that personality type is irrelevant. His frustrations at all the little things - any personality type can do that. I've seen INTPs in a bad mood doing that (i.e. getting mad to the point of yelling at you because of leaving a light on somewhere), and you really couldn't get farther from SJ than INTP. Also, being unemployed probably has a lot to do with his behavior; persistent unemployment can do a lot to a person's self-confidence, and can really hurt them mentally as a result.
But you asked about ISTJ-INFJ relationships, so I'll tell you how it would look at best:
A healthy ISTJ, in his situation, would be concerned about you, and would want to be helpful. Like Habba said, the ISTJ probably wouldn't like you living there, but then again, you don't like living there either - so the ISTJ would be understanding of the fact that the living situation was temporary. Also, because of this, the ISTJ would try to help you find housing, employment, whatever - or at least, he would check up on you to make sure that you were doing all that you can to reach your goals. He would absolutely NOT insult you and blame you for small, petty things and treat you like dirt. That would be counterproductive. If he were a good ISTJ, he'd see the problem and try to fix it - whereas what your mother's partner is doing is plainly counterproductive. And when a good ISTJ sees that what he's doing is counterproductive, he
changes tactics - which your mother's partner has obviously not done.
I doubt that my post has been helpful - most of what I said has been said already - but I will say that I'm sorry that he's been treating you so poorly

and although I'm not sure how you should respond to him, especially since there might be a possibility of physical violence(? if I read correctly?), I would definitely recommend talking to a psychologist, or any sort of expert on the matter. I'll bet there are a lot of good books about it? But honestly, this is to the point that I'm not qualified to be giving any sort of advice. So I'll shut up now.