I have a second home but my parents live in it and pay the mortgage

[shkcpa]

Mortgage interest is only deductible when paid by the borrower.  And real estate taxes are only deductible by the owner of the property.

[shkcpa]

The IRS also matches mortgage interest deductions with forms 1098 filed by the borrower.

[shkcpa]

So your parents aren't entitled to the deduction