Nervous about buying a house with tenants

[Alba Alamillo]

Hi everybody, 

I have been looking to buy a fixer-upper to remodel and flip.

My realtor has a listing from a lady whose husband died in February, she wants to get rid of their 3 properties and told the firm to please handle the sales for her.

They offered me a house that's not on the MLS, it has tenants and a month to month leasing agreement and the house is in excellent shape for having ben on rent for 30 years. (these tenants have only been there 2 years)

They are offering me the house 100K less than the comps. But with tenants included. I spoke w the tenants yesterday, they seem nice, they have the house in good shape, and they told me that they are in the process of getting approved to get a loan to purchase a property. I asked them why wouldn't they want to purchase the property they are currently leasing and the guy told me that they want to buy a one story house, the stairs are taking a toll on his knees.

2 questions:

1.- How do I protect myself from the worst case scenario? 

2.- This house is across the street from an elementary school. The comps that they showed me aren't in front of an elementary school. Do you know how much the price goes down if the house is in front of a school?

Thank you so much in advance. 

Alba