I don't know the details of your client, but it seems questionable if BOTH residences qualify as their "Principal" Residence that would qualify for the full exclusion, unless there was also "Nonqualified Use". It could happen, but be sure to check your facts before even considering such a thing.  Look up the rules for "Nonqualified Use".

The second house was within two years.  Did the husband move out for a qualifying reason that would allow a second home to qualify for the exclusion less than two year after the other home was sold?

As was mentioned, don't forget to consider the "step up" in Basis for the second home becauseof the death.