Whoa, that's a lot to unpack.
My first instinct is to get access into everything, with an emphasis on the financials. Bank accounts, tax returns, you name it. Because if he falsified tax forms and you've signed them (if you were filing jointly), then he's not the only one who committed an actual federal crime.
So, you need to know the extent of his lies and if any of them are worse than a fib here and there. You not being told accurate information about where he works/worked is one thing. But the IRS being fed that same cock and bull story is a whole other level of problems.
If his daddy is continually bailing him out as you say, then that also, potentially, creates an inheritance issue. If you and/or your children are expecting a payout when granddad goes to meet his maker, it may end up being a lot less than expected if your husband has been on the receiving end of cash bailouts for years and for thousands of dollars.
Oh, and if they hit a certain figure (can't recall it of the top of my head, but Google gift tax
), they may be subject to a gift tax. Which I will bet dollars to doughnuts he is ignoring, if that's a part of this mess.
As for your marriage (IANAD), I understand how you feel about your child together and trying to protect them at the cost of your own future. But consider the concept of providing a lesson to him or her. So consider this.
I have personally always despised the notion of staying together "for the sake of the children".
Because that puts an enormous weight on the child(ren). And it imparts one helluva lesson: that love and integrity don't matter, and an adult's feelings take a backseat to a child's. It also teaches that you can get away with pretty much anything and still stay in a marriage if there's a child.
That's a lousy curriculum for your kid.