Estate is beneficiary of a IRA. Three family members beneficiary of Estate. How do we take care of the taxes on the distribution?

My sister's IRA  is not a Roth. Her Estate is beneficiary of the IRA.  3 family members are beneficiaries of the Estate.  The Estate is getting monthly distributions for the next 5 yrs and the beneficiaries of the Estate split the monthly distributions. How do we report the income for tax purposes?  Thank you for any information. 

LaurieS