You will need to find a baptism for him to confirm parents as the DR you have does not list any relatives - how sure are you that that is his death notice. The parents attached were married in Wynberg- though I note the marriage lists the mother as Rachel Catharina Jansen not Rachel Jacoba Johnson. There appear to be no baptisms for children of this couple in the same parish (not indexed I paged through the register). There are a large number of un-indexed records - you may need to look through several Parishes to find the baptisms. The children don't appear in the Ring Book indexes but that may be because the Non-white parishes were not indexed. I would look through the Mission parishes in and around Cape Town to locate baptisms