@sigseher , while answer from @zomboo , expands on my original answer , interest deduction ( if you take itemized deduction) requires ONLY (a) ownership ( percentage ownership generally does not matter absent any restricting covenant between the owners) ; loan is secured by the property and you must have paid the amount. Generally if you are on the title, you also would be on the loan docs. ( i.e. you and the other owners are individually and severally responsible for the interest payment) and therefore any monies you paid for the mortgage ( to the extent it is interest for the borrowed monies ) is deductible.
Thus this could be your main residence or a second home / vacation home.
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