So, parents total debt is -
$61k to you
$90k to mortgage
$15k to IRS
$6k in personal loans at 22%+
$9k in collections (5k your mom, $4k your dad)
For a total of $181k.
The debt repayments are $900 per month, plus whatever the mortgage payment is. Income is $75k per year plus $600 per month rent.
Assets are a house currently worth $320k, potentially worth more but only with repairs no-one can afford, and a jeep.
I think you are overcomplicating things in your analysis. You want to reduce interest rates: OK, so how would taking out a commercial loan reduce the interest rates on the $61k loan you have made to your parents? You are charging them more than a bank would? If you are not charging them more than a bank would then you are worsening their position by making them take out a loan to cover the amount they owe you. (If you want your money back, that's a different matter. But you need to be clear that's what this is about, which you haven't been.)
Setting aside what you are owed, the first thing is for your parents to sell the jeep. Is it underwater? If it's not, sell it, pay back the loan on it, put the rest of the proceeds to other debt. If it is underwater, how much by? What's the interest rate on the loan against it? What's the math? Is the problem trying to organise a private sale when there is still a loan on it? If so, is the answer to find a buyer and for you to then bridge the loan (pay it off immediately before the sale and then collect from the buyer) so the sale can be made?
Do your parents have any other assets they can sell?
On the other loans, are your parents putting as much as they can towards the highest interest loans? How much is owed at each interest rate? As long as they are overpaying on their debts and not falling further behind, why not just be content with the progress made and just continue with that? 22% is horrible but there's a decent amount of income coming in. Don't subsidise any further, including co-signing loans, until you are sure that every possible penny of your parent's income is already being applied where it should be. If your parents have made the decision to buy comfort at 22% then let them: it's not your problem.