Thank you for the question, Empyrean.

Mishaela is correct here.
The plural for both nunh and tia is the same as the singular form (you will not add an 's').

Example:
My best friend was a tia for 15 years, before becoming a nunh.
Two tia left the tribe today after being defeated in battle by the each of the three nunh.

Also, both nunh and tia are not capped when used outside of names.

Hope that clears things up!