Give them notice rent is increasing by 10%, or whatever you think you can increase it to with repairs, with proper notice.

If you have a recorded mortgage and the county did not properly notify you about the tax sale, then the tax deed can legally be voided.I would get a copy of the tax collectors file and see if there is any mention of your recorded mortgage.I would talk to the tax collector and see what the story is and then inform your attorney.

Provide proper notice of non-renewal near the end of the lease term and then sell when they move out.

I am looking to make my first investment, and am curious about how to do proper market research.

A proper lease with separate option to buy I don't think is a starting out proposition.When it doesn't work with your cousin do you have a back up plan? 

Hello All -I have been running a relatively successful business for 15 years which has allowed me to save a lot of money while still living a good lifestyle.

As long as it was done properly, we'd be fine.

As others mentioned, you will still need to find an attorney or title company to ensure that clear title is properly transferred from seller. 

First check that the tenant was properly served notice to move. 

She is already on thin ice for other reasons.Looking back I see some red flags of her drama inviting life style that I overlooked initially.