see this article.
https://www.forbes.com/sites/janetberryjohnson/2016/07/27/tax-rules-for-renting-to-a-relative/#5dce5...
i'll give you the gist of what would go wrong
When a home is rented for fewer than 14 days during the tax year, the home is considered a personal residence. Mortgage interest and real estate taxes may be deducted as itemized deductions on Schedule A, and the owner is not required to report rental income.
When you rent a home to a relative, such as a spouse, child, grandchild, parent, grandparent, or sibling, any day rented at less than the fair rental price is considered a personal use day. To avoid having the rental days considered personal days, the property must be rented at fair market rates and be the renter's principal residence.
