I would highly recommend you create an LP agreement.

Review their management agreement.

They recently split up and the wife is asking to be removed from the lease agreement.

However, another factor was that the septic tank was shared with the neighbor and there were no written agreements in place as to who was responsible for expenses.

You've only owned it six months, so you probably haven't dealt with vacancies, maintenance, or capex, but you should be setting money aside for those things.Your partnership agreement (if you have one) should address exit options.

One thing I always remind people is it does not matter what is on a powerpoint presentation, the deal is dictated by whats in the PPM, operating agreement and subscription agreement. 

To minimize upfront costs, explore down payment assistance programs, creative financing strategies like seller financing, or rent-to-own agreements. 

Review their management agreement.

If it’s tied directly to the lender as part of your mortgage agreement, you’d probably need to negotiate with them or refinance with a different lender who doesn’t require that restriction.However, if the restriction is part of the property deed itself and was placed by a previous owner or another party, it can be more complicated.

At minimum, I am looking for the name of the deceased, a name of the personal rep/heir, and a name/contact for the attorney involved.