If your brother cannot be found, you may want to check with the IRA custodian and/or the financial advisor to find out if the IRA plan document includes any provisions for such a situation. For instance, some IRA documents state that if a beneficiary cannot be found, that beneficiary will be treated as if he/she is not a beneficiary of the IRA. If the IRA you inherited includes such a provision, you may be treated as the sole primary beneficiary - provided reasonable efforts are made to locate your brother.
Generally, the required minimum distribution (RMD) for the year of death should be distributed by all the primary beneficiaries on a pro-rata basis. In your case, your brother would withdraw 50% from his share and you would withdraw 50% from your share, assuming that you are supposed to receive 50% each. If he cannot be found, it may make sense for you to withdraw the full RMD amount, especially if it's possible that his share of the assets will go to you. This will help to ensure that the 50% excess accumulation tax does not apply to any amount.
To learn more about IRA distribution, check out Who Is The Beneficiary Of Your Account?, Inherited Retirement Plan Assets - Part 1, Inherited Retirement Plan Assets - Part 2 and Disclaiming Inherited Plan Assets.
This question was answered by Denise Appleby