Tony
The first three names were also Jan Antonie and Maria's children. I added the notes in [] to show the naming tradition in action. Sorry if it caused confusion.
The death notice doesn't state their dates of birth, probably because they were over 21. Baptism records show that Johanna was baptised in 1885, Hendrik in 1887, and Barend (I) in 1889. All in Ficksburg OFS. The other eight were under 21, and the official who filled in the form for Maria to sign evidently put in their dates of birth to show their ages.
Maria's death notice in 1913 indicates that only seven of her children were still living, i.e. Johanna Maria (Mrs Botha), Hendrik, Jan Christiaan Antonie, Josef Johannes, Maria Magdalena, Barend (II) and Maria Sophia. Once again, Barend's d.o.b. is given as 30.10.1904. The notice was signed by Maria's son-in-law, M.J. Botha, who appears to have taken over Jan Antonie's farm 'The Falls'.
Jan Antonie jr, Christiaan Jacob and Anna Cornelia thus evidently died between 1910 and 1913. It must have been a very hard time for the family, losing so many members in the space of three years, and making the youngest children orphans.
Johanna Botha died in 1925. Hendrik Petrus died in 1934. Joseph Johannes died in 1941.
Jan Christiaan Antonie (baptised in Ficksburg) married Anna Cornelia Sophia Pretorius in 1923, his home address being Wakkerstroom. He died in Volksrust on 25.07.1950. By then, Barend (II) was his only surviving brother.
I don't know whether ZARP enlistment papers survive. Hopefully, someone more knowledgeable will read this thread and be able to assist.