Steve,
The trio on the left I would suggest are native police officers. There is a very good engraving depicting that uniform that appears in The Illustrated London News of 25th October 1879, entitled Kaffir Women selling sugar-came in Pietermaritzburg.
I also recall seeing another engraving in the ILN of the REsident Magistrate in Ladysmith collecting the hut-tax accompanying by men dressed in the same attire.
John Y.