Maybe it's unrealistic to think I might help him heal, his kids heal

Ideally, the healing would have already been done, or at least, been well in the works before you married him.

If he is still obsessed with his ex wife and enmeshed with his adult children, there is not much that you can do. HE has to decide that he wants to live differently. Doesn't seem like he does.

He is never going to change by himself.  Maybe with professional help.  But not by himself

Entering a marriage thinking you can "fix up" your spouse is a recipe for disaster. It's best if you marry someone that you are pretty happy with, just as they are. It doesn't mean they are perfect, but you can live with their flaws.

You can't make him "live right" if he thinks the way he's living is just fine.  Marriage shouldn't be this hard after only 3 months. Your best bet is to cut your losses and move on.

No, I don't think you can help him heal. You might be able to encourage and support him, but he's got to want to make changes and he'll need professional help to do so.

I love my DH, but I stay with him because I want to, not because I have to. There have been several times during the course of our relationship that I was ready to walk away, and he knew I for sure would. One of those time I required, as a condition of my staying, that he get professional help. He did, and he took it seriously, and in fact six years later he still sees his counselor on an as-needed basis. This is from a man who, adamantly, would have nothing to do with counselors (methinks thou dost protest too much).

But he's got to do the hard work required. Most people won't.

My situation differs from yours and those cited here in some particulars, most notably in that I have only 1 male step, and when we married my financial resources were far greater than DH's. He literally could not afford to lose me. Which he knew would happen if he did not shape up. This is key--your DH has to know that either he straightens his shit out, or he is gone. You must be dead serious about this and he has to know it.

Even with the advantages I had, it took a few years to straighten things out. I had to overcome quite a bit of gaslighting and self-doubt. To this day I do not fully trust DH and it does not take much from SS to set me off. PTSD, I think. It was that bad. Also, DH does not understand why I don't care for his son. I sense he is a little sad that the two are no longer as close as they once were, and that he blames me in part.

But--success, mostly. At any rate, my life is free of step turmoil.