Doesn’t your current wife receive child support from her children’s father? Is her income not enough to pay her share of household bills? Or did you voluntarily take on paying for her and her family when you couldn’t really afford it?
It’s my understanding that the child support is pretty much by a formula in most places - if your income increased and/or hers decreased, you would owe more. And I think in most jurisdictions they don’t care about whatever additional obligations you have taken on since your divorce. You might speak with a lawyer about it but I don’t know that this will be fruitful. As for straightening out your finances:
1) You mention paying for S18’s college. He should be taking out student loans, going to a state school, working summers. You clearly cannot afford to pay for college for all these kids. They will need to take responsibility (I know there is still a parental contribution even so).
2) You mention school tuition. If your kids attend private school, they need to switch to public school. You don’t have private school money.
3) Cut household expenses. Dave Ramsey, Tightwad Gazette - you need to squeeze daily expenses to pay down those debts.
4) Raise income. Does your wife work outside the home? If not, she needs to find a way to bring in income. Can you increase your income in your job, or take a new job at a higher salary?
5) Take a second job or start a side hustle for some extra income.
