Hi Chris
As far as I know water isn't an issue on Ngwangwane Pass, but I have in the past struggled to find water in Thomathu Pass even in May, so its quite likely that it will be dry in August. There should be water available in the river on the escarpment above the passes.
As far as the passes go, both are pretty straight forward, Thomathu Pass has a path all the way to the top. Ngwangwane Pass has a path up to Bushmans Cave, then afterwards this disappears, but its a just a case of climbing a relatively short but steep grassy hill to the escarpment.
The last time I was up there, we encountered a few Basutho Shepherds, but they didnt approach us or anything, mainly just carried on with their usual business. But I suppose if you are camping on the escarpment you should be vigilant and take the usual precautions.