Keep in mind, gang, that Mormons believe that family is Everything, with a capital E. You not only are stuck with your family in this life, but for all eternity. I think a calm, reasoned approach here is the best choice, and since mom already brought up Church authorities, get the bishop involved.

I am aware of no aspect of LDS theology that is in any way against kilt wearing. But alienating your family? That's not so great.