How do you become an entrepreneur if you’re older, have family, loans, etc?

Would it be possible for just one of you to go full time into the business? That would take some strain off finances.

Also by having an income you get some tax benefits as you’d be able to write off the income from the initial expenses in the business.

As for 100k salary, that’s a tall order but it depends on how convincing your pitch is. If you have customers ready to sign orders and you just need to build a product. you might be able to find investors that will go for it.

Work nights and weekends. No VC is going to fund you at this stage.

What is your schedule ?: for creating the Minimum Viable Product, maybe it need needs just 20% of your time, and 100% of the software developers time ?

At this stage, do not quit for both of you. It is going to take you significant time to get to enough income to support you both. Nights and weekends.... you asked how people support themselves? They work 80 hour weeks with the other 8 hrs at night after the job and on weekends. It is going to highly stress your relationship with your wife, and your kids.

Both work, manage it, hire out the work. Or one quits - you rebase your living circumstances to fully live off that one salary.