I'm a beginner but it looks like the difference is:
kony: that, that one koni: those, those ones kesy: this, this one kesi: these, these ones
So kony and kesy are for singulars and koni and kesi are for plurals (same goes for bony, etc). It also helps me to think of the questions like this:
Kony ñuha korze issa? Is that one (over there) my longsword? Kesy ñuha korze issa? Is this (right here) my longsword?