Protect your investment first, negotiate a new lease & new rate if it suits your situation with the two remaining with the exact terms you want OR insist they collectively remain liable for the remainder per the lease unless they provide a suitable replacement acceptable to you.

But I'd still insist that something be done.

I have no idea whether this is a good idea , but shall I insist on have a copy anyways ?

The neighborhood around the university actually has a private patrol that is run and paid for by the university - students almost exclusively insist on living in this patrol zone.

They are probably pretty pissed at you because you rented to drug dealers and didn't manage the property well.I bet everyone else in the situation thinks YOU are the issue there and you insist everyone else is doing nothing to help YOU.Amazing.

Many entrepreneur articles and books I was reading at the time insisted on the need for an entrepreneur to "touch" as many people as possible and add value to those lives.

Appraisers - especially for government-backed loans like FHA, VA and USDA-RD - will insist on it. 

@Yonah Weiss gave us a very good link for an article on how to calculate the improvement ratio, but what happens if the property owner says that the land value is 0 and insists on that.

but if you insist, give me the 250k and i will find you 200k of property.

I am sure the seller is up front, but insist on tax returns.