Other people have to be paid, everyone doesn't work out of devotion and compassion!  

While I have compassion for the tenant, your grandfather does not have to accept less than the agreed upon lease amount just because of his status.

Where's your compassion? 

Seems like a good guy that may have a moral compass and still do the deal with me as a finders fee, but is there ways to give myself the advantage?

Human compassion trumps profit under these circumstances. 

I have a lot of compassion and empathy for other people.

Overall I would not turn off my moral compass in order to adhere to the lease 100% in this case.

You save eviction costs, free up her unit to get a new tenant faster, and you show her some compassion by helping her get out.

These tenants promised to police that they are moving out every time police was coming (now I am getting it - they are lying just to "buy" themselves more time for "free housing" opportunity, thinking people will continue to feel sorry for them just like landlords did and let them rent the house 2 years ago and now this is what landlords get back for their compassion :((.. ). 

There is zero place in business for compassion, get that out of your head and out of your business.