I think if you take the new job you will find a way to make it work.
If you stay where you are, you will continue to feel this is something you were forced into, that you never wanted in the first place. The decisions of the past will continue to rule your life and I don't think that can help but have a negative impact on the quality of your life and, by extension, your children's lives.
Kids are better off, I think, with parents who feel happy and whole than with having material things. You guys can make it financially. It might mean some drastic belt-tightening for all of you IF your ex doesn't pay (that's still not clear, either). But you aren't going to be homeless or eating out of a dumpster.
It can be a huge inspiration to kids to see their parents making a satisfying life for themselves. Especially in the face of other challenges. Do you want to teach your kids that they should never take risks, even ones that could better their lives dramatically?
I think you ARE sort of tending to cling to the "safe" option, which is understandable, but ultimately will hold you back. I think taking a little bit of reasonable risk under the circumstances would be a healthy thing to do.
Again, you are the one who has to live with the outcome, but if you were excited about the offer and the prospect of the job, that is not something you should dismiss as selfish.