Re: $152,500.00 debt
Which is it - 152,000 or 305,000? If the obligation is joint/several, then she owes it all, as do you. Of course, she probably has a right of contribution against you.
The answer is "NO" you cannot represent your parents, not unless you are a licensed attorney. And even if you are, it would be a bad idea to represent litigants in a case where you are very likely going to be a cross-defendant.
This raises another issue - why wasn't this issue dealt with in family court? Or perhaps it remains to be dealt with. If your divorce is not final (or at a minimum, if the property division is not final), then this likely needs to be resolved in family court.
Finally, there is no legitimate reason why an attorney would agree to represent your parents pro bono. Many attorneys would likely consider a contingency arrangement (where the attorney's fees is a percentage - typically one third - of gross recoveries). But ask yourself, why would an attorney agree to represent a creditor at no charge?
If the divorce is still alive, consult with your divorce attorney about the best approach.