@sjrcpa  Where do you see it's a second home?  I read it as this being the taxpayer's primary residence.  (" a house that is used as taxpayer's principal residence")  But the cast of characters here is confusing, and the mention of a "non-spouse" in the heading but not the text sets off alarm bells. It would be helpful to have a better description of the parties involved.  For example, "Dad lives with Son.  Son owned the house until he added his wife's name as co-owner.  Now Son is getting a divorce and Dad is buying out Ex-Wife so that he can continue living there."  But your guess is as good as mine.