IRA, Inherited IRA: Decedent RMD with Multiple Beneficiaries with One Uncooperative

Decedent (age 80)  has  not met their IRA RMD (age 80) and dies in 2019. The decedent's IRA has two beneficiaries with the interest divided evenly (50/50).   
One beneficiary establishes inherited IRA in 2019 and distributes 1/2 of the amount of the decedents RMD.
The other decedent is uncooperative and does not establish an inherited IRA. 
Therefore 1/2 of the decedent's RMD has not been met. 
There are three tax returns involved.  The last tax return of the decedent.  The beneficiary with the inherited IRA.  The uncooperative beneficiary. 
Who pays the penalty, the decedent's tax return, the beneficiary with inherited IRA, or the uncooperative beneficiary.