On the death cert there is always someone named who supplied the registry with the personal details of the dead person's place of birth and parents, etc. I wondered who that person was, and whether it also gives a relationship and address?
The death cert should also list the ages of living children, and whether male or female. Could you please have another look at it?

Secondly, Robert Christian's two marriage certs should also show his parents' names. On marriage certs the information is provided by the person himself, so they are usually more reliable than death details which are given by someone else who might not remember accurately. You said you have the dates of these marriages - would you be able to buy the photocopies if you don't have them, or are these what your contact is providing?

Sue