Both you and the seller need a keener eye I'm afraid.
The regiment on parade at Fort Napier are the 97th (The Earl of Ulster's Own) Regiment, the photograph dates from 1881, when they were deployed to Natal in response to the opening actions of the 1st Anglo-Boer War, however the regiment as a whole did not take any active part in the campaign.
The photograph gets touted around quite a bit as A Zulu War regiment or An infantry battalion, circa 1879. The second comment is o.k. The clue to it being post 1881 is the bearded Pioneer to the fore of the battalion, who is wearing his Good Conduct stripe on his left sleeve, rather than the right cuff. I have the photograph in my collection. The pale blue of the regiment's facing colour appear as a wispy-washy colour in sepia tone.
The graves are interesting though, not one I have.