The decedent's RMD is not more complicated than before death.

"For the year of the account owner's death, the RMD due is the amount the account owner was required to withdraw and did not withdraw before death, if any."

"which, after death, puts the onus on the beneficiaries (correct me if I am wrong)." Their part is the next year:

"Beginning the year following the owner's death, the RMD depends on certain characteristics of the designated beneficiary and the distribution option chosen by the beneficiary."

Decedent RMD is done before the account(s) get inherited or distributed, based on the beneficiary designations/eligibility/options and/or the estate/will. Brokers can be slow, but since Oct? That's just crazy. Then again, my client got an apology gift from Schwab for how badly their estate dept handled a spousal inherited IRA, but even then, it was under 6 weeks.