Those buttons are confusing. Normally, when you see buttons on a kilt it is to fasten braces/suspenders to. This was actually quite common in the nineteenth century, and I've seen it in some early twentieth century kilts, as well.

However, in those cases the buttons are always at the waist of the kilt.

On this kilt, the buttons seem to be at the hip line. There are two on the front of the kilt, evenly spaced from the center, and one right behind the lower buckle on the right hip. At least that is all I can see from the photos.

I cannot imagine what they might be for! But I do suspect they were probably added after the fact by the owner of the kilt, and not part of the original kilt.

This is a man's kilt, though for a very thin man. MacNaughtons, by the way, is the parent company of House of Edgar.

Aye,
Matt