You may find the article linked below helpful:

https://www.journalofaccountancy.com/issues/2009/nov/20091783.html

" The following summarizes the 15 letter rulings that were issued from Aug. 13, 2004 (the date final regulations were issued under IRC § 121), through August 2009 that have addressed whether given facts and circumstances qualify as unforeseen despite falling outside the specific- event safe harbors. In each case, the IRS found that unforeseen circumstances were present and granted the taxpayer partial gain exclusion relief under section 121(c); no unfavorable rulings were issued. The rulings can be broadly characterized as relating to (1) additional dependents arising out of marriage or other events, (2) environmental factors that detrimentally affect the quality of living in a particular locale and (3) job-related circumstances. Although the rulings may not be cited as precedent and do not establish a safe harbor of general applicability, they do provide a basis for understanding what circumstances the IRS is likely to consider unforeseen."

"Caring for disabled parent.  PLR 200626024. A taxpayer purchased a residence for himself and his three children. After the taxpayer got married, his new wife and her two children moved into the residence. As the result of an illness, the wife’s mother was partially paralyzed and moved into the residence because of her special needs. To provide the wife’s mother with the space necessary for her special care and accommodations, the taxpayer and his wife sold the residence and purchased a new home."