I'm a time-served brickie and would not use sharp sand on a wall, it's more for laying slabs with.
Coping stones can be bedded on with a "normal" mix of 5-1, that's 5 soft (yellow or building) sand to 1 of cement with a little plasticiser in the water.
Having said that, I (and most brickies) would use 3 - 1 because of the exposed position of the stones, ie taking the brunt of any rain or snowfall.