You try real hard to find a reason it's fair rent.
Otherwise, it's just "other income," and the interest and property taxes (both subject to limitations) go on Schedule A. When miscellaneous itemized deductions in excess of 2% AGI come back (is it in 2025?), the rest of the deductions go there.
Renting at below fair market, is considered personal use. If a taxpayer has any personal use of a dwelling that they rent, they must divide their expenses between rental use and personal use. They must divide expenses even if the dwelling doesn’t meet the definition of a residence. They may deduct only rental expenses on Schedule E (Form 1040). They may be able to deduct some of their personal expenses on Schedule A (Form 1040) if they itemize deductions.