Can I claim mortgage interest deduction if my name is not on the mortgage or deed but I paid all the payments and live at the house with my brother. We are 50/50 owners

The short answer is no. You must pay the mortgage and be an owner of the property.

There is a doctrine called constructive ownership where someone who does not own in name, can be treated as an owner.  You would have to take the deduction, get audited, and then go to tax court and argue your case.  The rulings I have read go both ways and depend on the exact facts in each case.

The case I remember best is a man, who was a recent immigrant, whose brother bought him a house since he did not have a credit rating.  The man lived in the home, performed all work, paid all the bills, and acted as the owner in every significant way, with the plan of refinancing in his name as soon as he could.  The IRS denied the deduction but the tax court ruled in favor.  Another case involved a man who moved in with his elderly father and began paying all the bills.  Since the man expected to inherit the house, and meanwhile was acting in every way like the responsible owner (paying all bills, etc.) the IRS denied but the tax court allowed.

However in other cases the tax court has ruled against the taxpayer.  It is specific to every circumstance.

Here your argument could be weakened by taking the home out of your name in preparation of moving out.

But in any case, taking the mortgage interest deduction means risking an audit and a trip to tax court to argue your case.  The black letter rules say you can't.

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.