death and the single owner

D, the 100% owner of an S-corp, passed away in 2018.  Ownership of the business passed to D's two sons who worked there (and were already participants) 50/50, and they also happened to be his 50/50 beneficiaries.  D was in RMD payment status, so we've been continuing to calculate his RMD each year and splitting it between the two sons.

Since D passed away pre-SECURE, are there any timing issues I need to worry about for the distribution of D's entire balance?  The post-PPA plan document says that the beneficiaries "may" elect the 5-year rule.

Thanks.