Would Minh or Manh be a better surname for a Vietnamese character in a book I’m writing? Would this be okay as surnames or should I look into different ones?

Either Minh or Manh is not a common surname in Vietnam. Maybe in ancient times, but now they are mostly used for names. Most common surnames for a Vietnamese person are Nguyen, Tran, Pham, Le. I’m saying this as a Vietnamese person named “Manh” myself.