First off, Native Americans is NOT what the people wish to be called..
Because we are "Indigenous" or) First Peoples.
To be even more correct than all the rest.. Human Beings
Secondly, What we wear at Pow Wows and Functions of the people..
Is NOT called costumes! Costumes are for plays and Halloween and fancy themed parties.
What we wear, correctly is called Regalia.
Because we wear our heritage of living history.
Among most tribes and Nations of Indigenous, if a individual has been taught in the ways and customs of the people of their tribe or Nation, and has participated within their cultures. Then they have earned the right to be called among their people..
Respectfully, depending on the age grouping..
40-50 plus, Aunties or Uncles.
60 plus usually Grandmother or Grandfather.