If you look at the rules they would not qualify for either stimilus, this is in the case where they recieved it  based on the 2018 or 2019 return when they shouldn't have, because they were deceased in 2019.    I am not 100% sure but because they became deceased in 2020 and they are filing a joint return they should qualify for the stimulus.  Just like a dependent exemption or anything else you don't prorate their credits you get it for the fullyear.   If they became deceased in say Oct of 2020 wouldn't they get it, you don't prorate it.  You would need to research further but that would be my understanding