Question on 1099-S inherited sale

My FIL passed away in 2015 and left an apartment building he inherited from his mother to my MIL.  The apartment has been severely neglected over the years and was too much for my MIL to keep up.  No money was made off of rent in the time my MIL took over.  We were never involved with the apartment or received any income.  My MIL wanted to set the apartment up so that my wife would inherit the property once my MIL passed away.  Since 2015 the property has been tied up in my FIL's estate which could be a complication.  My MIL doesn't handle dealing with settling estates and grief very well.  My MIL decided to sell last summer to be rid of the headache and split the sale with my wife.  She finally settled the estate and sold the property promptly afterwards.  We got a 1099-S and was told by the closing attorney we would get one but no mention of how this would be filed.   How would this be reported?