Retirement tax questions

Thanks for your replies but I am not asking for an opinion on whether it is more advantageous to distribute the income to avoid the estate's tax liability. There are reasons why it is not in this case. Your response suggests that I must exercise my discretion to ensure the beneficiaries incur the tax liability rather than the estate. That doesn't make sense to me. I'll try to re-post my question to solicit additional input, but again, I appreciate your help.