Apart from all else, I am certain that you are mistaken in this. The Mask Salesman uses healing magic to create the transformation masks, he seems to care about the damage that Majora's Mask can create, and at the end of the game he is quoted as saying "Your masks are filled with happiness. That is truly a good happiness". As for being a decendant of that tribe, I wont deny that it is a possibility, but because we have no evidence neither here nor there, it becomes irrelevant.

As for Majora's Mask, we have little Information of it besides what is directly quoted, shown in cutscenes or in gameplay.