Welcome to the forum, great to hear from you. You may know that there is a reference to Sapper Cuthbert in a little book called the "Red Earth" published in 1996 by the Royal Engineers Museum to accompany an exhibition of the RE and the Zulu War. Cuthbert was one of those who came up with Lt. Chard to repair and maintain the ponts at Rorke's Drift.
In the section on Sappers at Rorke's Drift it says "The four sappers received orders on 22nd to join No 3 column at its new camp at the foot of the hill Isandhlwana, some ten miles up the road from Rorke's Drift. The four men climbed into their empty wagon and the native driver set off for Isandhlwana. Later that day, having successfully lured Lord Chelmsford and half the column away from Isandhlwana, the 20,000 strong Zulu army swept down on the camp which, despite of fierce resistence was totally overrun, the four Sappers being amongst the 1,350 casualties, only 78 Europeans escaping."
I imagine they must have been located in the camp itself. But others may have a better idea of where exactly.
Hope you can tell us more about Sapper Cuthbert.