whose name(s) are on the property title? is the mortgae secured by that property?
The IRS does not have a minimum number of days you must live in the home to count it as a "second home."
However, you must be the legal or beneficial owner of the home to deduct the interest. A legal owner is a co-owner on the deed. A beneficial owner is someone who, although not on the deed, has an ownership interest as determined by the facts and circumstances.
For example, Adam bought a house for his brother Bob, because Bob was a new immigrant with no credit or work history. Bob lives in the home with his family, pays the mortgage and all other bills, accepts the duties of a homeowner to perform maintenance and repairs, and plans to transfer the deed and refinance in his own name as soon as he has good enough credit. The Tax Court ruled that Bob was a beneficial owner.
Besides being the legal or beneficial owner, you must also be the person who actually pays the mortgage interest.
And to deduct property taxes, you must be legal owner against whom the taxes are assessed. The Tax Code does not include a property tax deduction for beneficial owners.