Yes TreeSpirit because I have found nothing besides the info on Geni and Wiki except for the baptism you have posted. I use the link given to look for baptisms of the other children with no results so far. I have looked through the civil deaths for both Hendrik and Anna, nothing so far. Also looked thought the civil marriages for OFS and the Cape found nothing.
Even went as far as collecting all the Hendrik Cornelis's death notice's that I could find, no results. I then looked for all the Jacob van Reenen Van Niekerk's since someone said he was the father. Hoping to find Hendrik, came up empty.
I though if I could find their marriage it might give me a clue to his age and place he was staying before marriage.
Another thing the parents that one tree gives him had a son Hendrik Cornelis born 1850, he to is a mystery. Found his baptism but nothing else, at first I was thinking he could be the Hendrik born in 1858. But then maybe the one in 1850 died young and they gave the name to the one born in 1858. But that still does not help, for I cannot find a baptism for the one in 1858.
Now back to Hendrik and Anna's marriage, Anna was born in Beaufort West her mother died when she was about 7 and her father remarried. So her baptism should be there in Beaufort West records, but I have not found it. I then looked for her marriage in Beaufort West thinking she might of married there, came up empty.
It is as if they simply disappeared.
I found a baptism record for Hendrik and Anna's son Jacob van Reenen van Niekerk b. 1897 in some other Estate file, this was a few years ago but did not keep the file since these van Niekerk's are not directly linked to mine. And I cannot find it again, all I remember is it was a estate file for a woman and it was from the OFS. I also remember thinking it odd that his baptism record would be in her file for I could not find a connection to him.
As for Hendrik and Anna's son Jacob van Reenen van Niekerk b. 1897, I have looked for his baptism in the church records but it is not there. According to the record I found he was baptized in Boshof in the N G Kerk. I have his civil death notice and marriage and children all in Johannesburg, have his grave picture as well. But the only mention of his parents is on the baptism record. And the fact he named his son after his father.