Upon the death of the original owner, the designated beneficiary(ies) becomes the owner of the IRA and has the responsibility to take the RMD in the year of death if the deceased didn't do so, and the beneficiary would also have the responsibility to rectify any shortfall because of missed RMDs. Each beneficiary should take his or her share of the distributions for the shortfall as soon as possible after the shortfall becomes known, and it can be taken all as one lump sum.
Prepare a schedule showing each year's RMD that the deceased should have taken and, if more than one beneficiary, show how each of the year's RMDs are split up among them. Using the appropriate year's forms, each beneficiary completes separate 5329s for each year that a shortfall occurred, and requests penalty abatement on each of those forms. Because these are for prior years, the 5329s must be filed separate from the 2019 return and must be paper-filed, e-filing not allowed. I'd file them all together with an explanation that includes the request for abatement and the schedule showing the shortfall and its allocation to each of the heirs.
Going forward, each beneficiary will also follow the distribution rules for inherited IRAs by nonspouse beneficiaries of decedent that was over 70.5 years of age and dying in 2019 or earlier.