OK, you've got a mess.
Here's how I see your financial breakdown:
-Her mom GAVE her $80K, she CHOSE to GIVE it to this project. Bad decision.
-Your parents LOANED the two of you $80K, with 4% interest secured by the house. You BOTH have an EQUAL obligation to repay this, though EACH of you probably owes the ENTIRE debt, regardless of what the other one does.
-The previous owner GAVE you $30K, which you CHOSE to GIVE to this project. Bad decision.
-You BORROWED $60K additional from your parents on a verbal agreement @ 4%, which you CHOSE to GIVE to this project, and YOU have an obligation to repay it, not her. Bad decision, for both you and your parents.
-BOTH of you borrowed an additional $48K secured by the house. Again, you BOTH have an EQUAL obligation to repay this, though EACH of you probably owes the ENTIRE debt, regardless of what the other one does.
By my calculations, you share $128K in debts secured by the house. Figure out how to repay it- probably from the asset you share (the house).
Additionally, you have a personal debt to your parents of $60K, and she has a personal debt to her mom of $80K. The right thing to do for each of you would be to repay these debts.
If the value of the property is $240K, it won't be possible to repay the entire $268K in debt. The secured debt will have to be first, the personal debts to your parents will be last. Sadly, everyone is about to take a beating, including your parents.
It makes no difference how all the rest of that money was spent. Work it out, and take your beating. Bad decisions to tie consumer spending (CC- unsecured) to secured real property. The lesson for both of you is to define things carefully up front, in writing, and watch who your partner is. Oh, and HAVE an exit strategy.
I understand your attachment to the house. You are NOT in the position to own a house right now. The closest you can come to this is if your parents would buy it, and you can consider buying it from them later. If I were them, I wouldn't do it unless there is a VERY STRONG likelihood that the property is going to increase by 30% in value in the next few years WITH NO FURTHER EXPENDITURES.
Tax assessment is meaningless to determine value. The $240K appraisal is the best you've got, but I certainly understand her disappointment in this number, and think a second opinion is a really good idea.
Sorry to be so blunt, and sorry for the current painful situation you are in. Good luck!