muzoman on Family Tree Circles

This is an intruiging and somewhat sad story from someone who is trying to to trace his grandfather's heritage. I have in my possession a copy of a birth certificate that says my grandfather was born on the 25th September 1904 or 1907 at Market Street, Pretoria. His parents are listed as a Christopher Barnes who hailed form Queenstown and who was a blacksmith. His mother is listed as Annie Barrett or Barnett and whose place of birth is only written down as 'Cape Colony'. I don't know if at the time the mother's maiden name was used as opposed to the married name. Perhaps they were not married. So far so good but here is where the intrigue starts. When my grandparents got married the surname used was 'Schnittker' and their 4 children [only my mom still survives] grew up as 'Schnittker' and were all born before the start of WW2. When my grandfather enlisted or maybe he was called up the documents show that he did so under the name of 'Barnes'. He served in North Africa and upon return was involved with the construction of the Storms River Bridge which was being constructed by Italian POW'S. Whether this is totally true I do not know. He then disappeared and it took my grandmother many years to track him down. It had a reasonably happy ending in that they spent the last years of their lives together. My grandmother at this stage having permanently used the name Barnes. This might sound odd by I always questioned this change of surname and could never get to the bottom of it all. His children, and to this day my mother firmly believed that he was a Schnittker and that he might have been adopted. But the birth certificate proves categorically that he was born a 'Barnes'. I have checked historical shipping lists for a Schnittker family that may have migrated to SA and the only thing I can find is that of a Robert and Anna Schnittker who sailed to Africa's West Coast ie. South West Africa and now Namibia. So no Schnittker' landed in SA. One of the stories told to me was that he got adopted because his parents were killed in an accident. But which set of biological parents? If his biological parents were in fact Christopher and Annie Barnes as his birth certificate suggests, did they perhaps decide to move to SWA/Namibia where something happened to them which then resulted in his adoption by a Schnittker couple. Who knows but it is all a mystery. One piece of information I did find on one of the journals posted to which a Michael Barnes responded a Morne Barnes was that he had a book written by Pamela Barnes and published in 1984. I researched the title and found it listed on Amazon but it is out of print. What I did find however is that the resellers provide single word reference points. I was amazed to see a reference to 'CHRISTOPHER'. But when one clicks on it nothing happens. So where does one go from here? I have the ISBN details of the book by Pamela Barnes but I doubt it if they will print a single copy as it is listed as out of stock. What am I trying to achieve? I believe that my grandfather was born a Barnes. I want to find out what happened to Christopher and Annie and whether anyone can throw some light on the adoption etc. Perhaps there is someone in SA who may have some information. I live in the UK by the way. Any information supplied will be most welcome and I would really appreciate any form of collaboration.
It makes no difference to my surname except that the information on my parents' marriage certificate as to 'spouse maiden name' and 'mother of child' on seven birth certificates maybe should have read 'Barnes'. Not to mention a very few others in SA who might not know that they are really 'Barnes'. I however see no reason to upset the apple cart. It will just be great to find out what really happened.

Thanks to anybody who can be of any help and regards to all the Barnes' in SA.