My strong suspicion is they are taking advantage of the current weak owner and they know they are getting a free ride that they won't get anywhere else, and that the ride has come to an end. 

I should have taken their late rent seriously after the second month they were late... they are definitely taking my kindness for weakness.

.Edit to add a quote about luck: "I believe luck is a concept created by the weak to explain their failures." - Ron Swanson (Parks and Rec, lol)

If you show weakness and back down to the tenant's threats, they will walk all over you - and it may also be used in court to show you allowed the behavior, so now you can't complain about it.

It sounds like you have compassion, and they smell your weakness.

The current weak link of the company seems to be on the leasing side, with all of these new properties closing or renovations coming to completion we had a ton of leases that now needed to be done for our clients.  

Sometimes your greatest weakness is also your greatest strength!

Some assets are very weak today, including retail, hotels and nursing homes.

Weak case in front of a judge if they say they can't stay but also won't leave.

Just understand what you're doing, why you're doing it and what the tradeoffs are.Here's my philosophy on hiring professionals: I exploit my strengths and hire out my weaknesses.