I don't like the third strap/buckle. I don't see it as useful, and it is one more thing to snag on. It does make a certain amount of sense on a higher rise military kilt where limited sizes are to fit widely varied groups of men in many different sizes. But with a modern civilian style (2" rise) kilt, it seems pretty much there "just to look" at from my point of view.

I vote two, not three. Less work for Gran too. (I am sure She does not mind the extra work, else She would not have offered to make them in the first place)