The last two years I've paid the mortgage payments.
That doesn't matter. Since your name is not on the mortgage, you do not have a legal obligation to pay it. Since your name is not on the deed, you do not have a legal obligation to pay property taxes either. So you also can't claim property taxes.
We consider ourselves 50/50 owners even though my name isn't on the deed or mortgage.
The IRS would most likely consider exactly the opposite, since physical action was taken by you, voluntarily, to divest yourself of any legal obligations to the property by removing your name from the deed, as well as the mortgage.
Your brother, the actual legal owner, can claim the mortgage interest and property taxes though, regardless of who may have paid it, since he is the only one legally obligated to pay it.
