"Since they're not in business, they shouldn't be preparing a 1065 with any amounts on it anyway.  Zero income, zero deductions, attach a statement that says, "personal assets only."  Substance over form. "

I learned these facts today from the attorney. I think it is a business but I'm curious about your take:  "Son and Daughter are renting the property to their Mother on an arms-length basis with an executed residential lease and fair market value rental price for her part-time use.  Family members also use it occasionally.  In addition, although the property has not yet been rented to anyone other than Mother, it may be, especially if it ends up being vacant too much or maintenance costs become exorbitant."