I wanted to ask the same question, but I thought to leave it alone.
I'm not understanding if there's a connection being drawn between ISTP and alcoholism or if you're asking for help in reaching an ISTP alcoholic. I think those are two separate issues.
I'd first address the alcoholism problem. I personally don't think this is time to leave a person unsupported, even if they're a type that typically doesn't respond well to this kind of intervention. If he's at all aware of his behavior and has a smidgen of motivation to change, then don't abandon him. IMO, personality type is irrelevant at this point.
If the wife and children are in any danger, then they need to leave immediately. There are many websites that gives advice on how to deal with the general problem of alcoholism. Aside from this very meager advice, I'd seek professional help.
I am in no way saying they are alcoholics because they are ISTPs. I am saying that, in my experience, at least one ISTP was resistant to the idea of treatment, 12 step groups, etc. until the day he died due to complications of alcoholism.
In this situation, I don't want to repeat the same mistake. I want to give my brother one chance - and only one from me - to get his shit together. I'm concerned that on some level he thinks none of us cares... noone seemed to care what happened to my dad.
As to typing them... my dad took the MBTI as part of a severence package and typed as ISTP. I gave my brother the Kiersey (unofficial version) and he typed as ISTP. I could go into superficial traits (epicurian, egalitarian, detests authority/rules, likes beer/darts/cars, etc. but he's already taken the damn test).
My sister in law asked if she's doing the right thing by telling him she'll leave with the kids if he doesn't go to rehab. I said she is.
She is not thinking rationally at the moment and keeps going back and forth. She still thinks she can get him to change his behavior, if only she could find the 'secret password.' She is alone with him in Texas... she has no one else to help. At this point I'm rambling on a tangent. I've told her that any choices she makes from this point on should be solely about what is best for her and her children, and not about what may or may not get the desired response from my brother.
He's about to lose everything; this is just my 11th hour brainstorm to see if maybe, possibly, there's a way to get him help.
I know he has to want it... I'll ask her to call a professional interventionist and let them advise her.