Hi Donald. To answer your question, it will largely depend on what type of loan that you do. If you have a 2 year rent history or more and you pay the rent using a check or money order to the landlord, you will have a papertrail for proof of rent. If your brother pays you cash for his half, you will not have the proof that an underwriter/bank will feel comfortable with. Also the bank/underwriter is going to ask for your full tax returns to see if you told uncle sam that you were collecting rent.
However, if your brother pays you by check or money order and you have been sharing the rent long term than the bank may consider his rent towards your monthly income. The most important factor is weather you can afford the monthly payment without your brother's income. If you can't, I would suggest that either you find a home with a lower payment or you add your brother to the loan so you may use both of your incomes. Because you are buying a single family home, relying on your brother's money to make your payment is considered risky to a bank because your brother could move out at any time and leave you with the full payment. And if you need your brother's money to make the monthly payment, you may be over extending your self. I would suggest that you talk to your family members and find a loan officer that your family has used and trusts, then sit down with that person and go over your situation so you will know what your getting in to. Remember that if the payment seems too steep for you, it usually is!