The foundation is so bad the house has shifted and I’m going to be spending nearly 40-50k to get this remediated.

When violated, contracts state what the remedy may be.

Unjust enrichment is an equitable remedy.

The overall experience was ok, I think the Morris group realized that partnering with new construction groups is a cleaner approach rather than selling dilapidated properties and trusting rehab teams to remediate the property in earnest. 

Now, if the seller was free & clear (no mortgage) when he sold, the seller could enact whatever remedy was provided for in the Deed of Trust, if he was savvy enough to even do a Deed of Trust.

If, after the first ten (10) days after you take possession of the Rental Unit, it becomes necessary for us to undergo including, without limitation, prevention and remediation in your Rental Unit and/or on the Premises, you will be held financially responsible for reasonable costs thereof, paid as Additional Rent.

BRRRR challenge 1 -- Mold Remediation - Any insight?

My guess is You will need to go through a foreclosure process in this situation as a legal remedy.

If the mold is caused by a leaking pipe or water getting in from outside, then you should hire a contractor to stop that intrusion immediately, then dry out the home and remediate the mold at your expense.I also recommend reading and sharing the EPA Mold Guide.

What if it is your unit causing the water leak and there is mold and it's a $100,000 remediation that requires living elsewhere for 2 weeks while it is cleared.