Karnali....i agree with you of your perception of Thakuris about Thakuris thinking themselves as " hune khane, dekhya sunya haru". Genetically, thakuris could be mixed with Magars or something...some do have some magar like physical features.

Anyways....coming back to the topic of names for mother......it seems like the sound of "M" is the first sound a child makes and the first thing he wants to call is his monther and hence all the cultures have their Mother sound starting from "Ma".

Now, may be the second easy sound for a child is "ba" and hence the sounds "Ba, Pa, and Pha is ther for fathers name.