I have sent letters to the last known address, contacted the city and the county & no such luck of reaching the owners.

You'd be able to get a letter of environmental protection saying you did illegal work, got caught, then had to hire a professional to come in an clean up the mess. 

You'll also likely have to write a strong letter of explanation to explain why your properties went into forbearance and why it's not likely you'll go back into forbearance. 

The question I have is whether I should send a courtesy letter ahead of time letting the tenant whose lease I won't be renewing know that they need to be looking for new residence as long as the sale goes through, or if that is too much of a risk since things are not finalized yet.

Or, hire a mortgage servicing company some of which would send out foreclosure letters and enforce and start debt collection process etcHow the best way to handle the no insurance coverage issue and tenant not paying property tax once for all ?

There is no such thing as a pre approval letter to purchase MF. 

Many or all the the units may already have signed leases, but every time we purchase an apartment building we give every tenant a copy of our lease even if they don't sign it so the tenants know our House Rules, how we start the eviction process when their rent is late, who to contact when they have any issues, etc.When we purchase a property we always write a letter introducing ourselves.

Those large issues being the following:The basement that is mostly underground is unfinished and the house sits on the side of a hill, so when it rains, the water builds up around a few areas and eventually over time will penetrate the concrete blocks in the basement causing mold to grow on the wall and make the Drylok start to peel in the areas that have the moisture issue.

Should I have a letter of intent prepared?

It’s over Supreme Court blocked it so you should be able to get an eviction and writ  https://www.supremecourt.gov/o...In Wayne township the judge would set compliance hearings but would never rule - kept giving tenant another chance.