I want to emphasize more strongly something that both xmasbaby0 and pk mentioned, because I think it's a key consideration in answering your question.
In order to claim the mortgage interest deduction, you have to meet two basic requirements. First, you have to be legally liable for the payments, which means you have to be listed as a borrower on the mortgage. If only one of you is listed on the mortgage, only that person can claim the deduction.
Second, you have to have actually paid the interest. That means that you have to decide who is going to claim the deduction before you make the payments. Only the person who actually paid the interest can deduct it. Even if you are both liable for the payments, if your father made the mortgage payments, he can't decide later to let you claim the interest deduction.
