I'm with Alex, I think you're helping them in wrong way and your plan could end up making your relationship with your parents difficult. Assume you lend them all this money and six months later they still need more money to keep the house or business. How are you going to feel then? Are you going to loan them more? What if, instead, you decide enough is enough? How are they going to feel about that? Are they going to feel abandoned because you've loaned them money before and now you not willing to do so?
What if the market drops, are you sure you are not going to feel any resentment? Often what we say we will feel and what we actually feel can be two different things. This path leads to so many possible problems, all in hope that one property will rise in price within 2-3 years. Not worth it.
The fact that so many here have suggested that the property should be sold is a good indication of what your parents should do. Convince them to sell the property and do not lend them any money. It’s harsh but far less stressful.
Best of luck, you have some hard decisions to make.