Multiple borrowers.
Even though there may be more than one borrower on the mortgage, the lender is required to prepare Form 1098 only for the payer of record, and only if such payer of record is an individual, showing the total interest received on the mortgage. Even if an individual is a co-borrower, no Form 1098 is required unless the payer of record is also an individual. Just give a copy to the other borrower and each of you enter your pro-ratter share of the mortgage interest based on your ownership interest.
You and your brother may deduct the portion of the interest that you actually paid if you Itemized your deduction. If your brother doesn't live in the home permanently, he has to use it at least 14 days a year to be able to deduct his portion of the interest paid.
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A rental property is a little more complicated.
If you prepare a schedule E for the property it would include the rent received and the mortgage paid (Along with other possible income and expenses).
If you have more than one person involved it now becomes a partnership. As a partnership you can properly allocate the results from the property to each individual. A partnership requires a separate tax return.