Do you have any recommendations on how to remedy the situation?

If not, I would still recommend going ahead with a professional cleaning company that has experience with mold remediation (make sure they send before and after pictures as well), if you really wanted you could give a small credit to the tenant to make them happy as well but 100% not required. 

Once we were aware of this and the owner refused to properly remedy the issue we had to cut the property, we actually cut the client and his 6 other listings.

We were told we have mold in our basement and got 1 quote for mold remediation and it came back at $5,500.

@David Kirkpatrick hmmm... here are the problems I see with this scenario (and that you need to remedy).

The owner has 30 days to remedy the situation.

Child sustained broken leg and concussion from falling through rail spindles that were too far apart. 3 days in the hospital, surgery

I had a remediation contractor come out, and he told me the levels on the report is what he'd expect from a basement in Portland, and any amount of washing / bleaching wouldn't reduce the levels much long term as more moisture would enter the space up from the slab because concrete will always give off some moisture, and he couldn't really recommend much remediation. 

In December, one of my tenants went into surgery and has not been able to pay rent for December or January.

.), not allowing access to the property (these are often vacant land deals or sometimes vacant houses), wanting to close remotely/ use a mobile notary or their own title company that is also out of state, wanting only cash offers with few contingencies, no “for sale” sign at the property, willing to sell the property for less than fair market value for a quick sale (often there’s a story that they need money quickly for their husbands surgery or some other emergency), they often have a foreign accent, and only want to communicate over the phone or electronically (for some reason they always use an outlook email and many prefer to communicate through WhatsApp).