It is my understanding that the basis of qualified joint interests in property will be adjusted to FMV (or a step up in my case) at DOD to extent they are included in the estate of deceased spouse even if no Estate Tax return is filed.   I believe this relates specifically to the Building Sale.   The Sec. 1245 Assets sold from the S Corp would also receive a step up in basis at DOD because wife inherits the LLC.   Husband dies May 9th, 2018......business and building sell Sept 1, 2018........FMV easy to determine.