@shyguy,
You're not going to get any younger and you're not going to get a do-over.
But you can still salvage things.
Your wife needs to get her license back. She needs to be actively working toward that. And if she can't get her nursing license back then she needs to find some other way to do similar work, perhaps as a health aide.
It's been four years. I have been through long-term unemployment and it truly stinks. The greatest advice I can give is that not looking for work is an automatic "no". At least trying to get a job is better than not trying.
For her, it may mean an employment counselor to help her look into her options. Even if she ends up taking a drastic cut in pay, that beats the hell out of zero.
Four kids, eh? Unless they're quadruplets and just born, there are care options. It's still the summer so that's not so easy, but once the school year starts, isn't at least your eldest in school part-time? Younger kids can go into day care or preschool. And yes, I am well aware this all costs $$. And it's possible your wife's salary would be 100% committed to child care. So be it. At least she would be providing financially.
I am also suggesting outside care for your kids in order to remove that as a potential excuse for not looking for work. "Oh, I can't send out resumes, I have to take care of the kids." <-- that's a lame excuse, particularly when they're older. But even the parents of newborns get a little down time for naps, and sending out resumes these days is a matter that's no more difficult than sending emails.
Interviews take time away, yes. Hence get into starting to set up care arrangements. Because you'll need them when she starts working again. There is an enormous nursing shortage in the US and in a lot of other parts of the world. If she can get any sort of a license at all, then she'll get work.
She doesn't have to be unemployed forever. And you don't have to be the 100% breadwinner forever, either. But someone's got to break the inertia.
If she won't, then that person is you.