You can't go after them for violating the lease agreement. - If you take ownership, and if the lease is a month-to-month lease you could choose to not renew and get them out.I am not sure how good of a deal this is or if you are in contract but if I were a seller and had other interest I would be considering different buyers. 

Either way it's important to find an attorney and get active on this so you can surf the wave rather than continue to be hit by it.In general it's been my experience most people that go through the trouble (read "time, money and back ground checks and CPE") to attain/maintain any credential or license are keen not to have it revoked due to ethics violations, acts of moral turpitude, criminal convictions, as that can have a permanent deleterious affect on their future career prospects. 

I don't know what paperwork was signed or what evidence you have but I would contact the former "tenant" and let her know she violated the agreement and has caused me some major losses.

Make sure it explicitly explains the process for termination if you are unhappy with their services, but especially if they violate the terms of your agreement.3.

Building Code Violations on record at the Muni?  

You may be in violation and subject to fines and/or eviction.

(Applicant had just traveled from several states away and ended up being an excellent tenant)We have to stick to our criteria, so everyone is treated the same. no judgement is made that could be in violation of fair housing.

After finding out there is an unauthorized animal on my property, I send a demand letter to the tenant stating their violation of the lease agreement.

If we keep it as a rental we can get 1750-2100 per month in rent.This violates the 1% rule.

the main issue is you have to owner occ.. if you rent a room out I really don't think that is a violation..