Many of these decisions are not possible for a stepparent to do, or a couple recovering from a divorce/debt.
In the OP situation, it was someone with more money (but presumably no kids he was supporting) marrying into a family. Do you really expect him to say on day one “Hey, you have these 3 kids and you/we should be putting away money for college immediately. Oh, and we should all live in my very small house because it is our starter home. And I should sell my car that I could easily afford when I was single but that money should go to college.”
That’s just not realistic.
Should they not have gotten married? Probably that would have been the best financial decision for college for her kids. Should they get divorced? May not work at this late hour.