My advice would be to see if you can purchase the plans only. 

You pay off $6M mortgage, have $4M in “cash” but only a $2M taxable gain ($300-$400k?).

This will be a long term rental that we plan to keep for many years. 

Pointed out the clause in my lease and they have been paying it for a little bit.

Balloons coming due with higher interest rates, China market, China production, Manufacturing production moving back to the US, Worker shortages, Workert pay hikes, Ukraine/Russia food and fertilizer misses, Oil prices increasing due to the OPEC Q1 production curtailments in place, Houthi issues, Panama Canal Water issues, Illegal immigration impact (buy one of those office buildings and rent for $10mm per year for Illegal housing, take advantage) social benefits required, Climate change believe it or not- Buy or sell into that thought process,  US politics, Baby boomers leaving workforce and needing more benefits, Baby Boomers moving from Stocks to Bonds,  etc.I agree things will get worse, but that means more investing opportunities. 

I plan on rehabbing the property and refi within a year.  

They listing had a failed pending sale and eventually my brother talked them down to $400k sales price planning to buy it on his own.

It will cost her thousands to move, she will probably have to pay more at a new place, and they probably won't accept her rabbit, either.Know our value and charge it.

Now, when communicating with the tenant I find a specific date on when they will be paying.

We have had the same tenants since we leased it in 2022 and fortunately they have been great- minimal maintenance requests, very easy to communicate with, and pay on time.We have a 30 year fixed mortgage on the property at 2.875%, the property cash flows about $1,200/month, and there is roughly $200,000 in equity in the property.