For the decedent's year-of death RMD, yes, the year-of-death RMD can be satisfied by the beneficiaries in any combination since it's not a beneficiary RMD. Section 1.401(a)(9)-5 Q&A-4 says that "that amount must be distributed to a beneficiary" [emphasis added]. So if one beneficiary took a distribution that was sufficient to satisfy the decedent's 2017 RMD, no other beneficiary needs to satisfy any portion of the decedent's 2017 RMD.
Beyond that, hopefully the inherited IRA was split into separate inherited IRAs for the beneficiaries by December 31, 2018, otherwise the beneficiary RMDs will all be based on the age of the oldest beneficiary rather than on each beneficiary's separate age.
