In South East Asian cultures in particular and Asian cultures in general, it's considered very rude to address people who are older or in higher status than you with only their names, such as when Raya calls Tong or Boun calls Raya or Raya calls Sisu (a deity-like figure) with their names only. In Asian cultures usually you would address people using familial relationship: you would call a person who is around your age or slightly older than you with "brother/sister", person who is in the range of your parent's age with "uncle/auntie", person who is older than that with "grandpa/granny", and revered/high status/deity figure with something like "master/lord/lady". So Raya would call Tong "Uncle Tong", Boun would call Raya "Sister Raya", and Raya would address deity-ish Sisu as "Master Sisu" or "Lady Sisu".
Though this would, of course, assume that Kumandra is in what is known today as South East Asia. Even if it were, there's nothing to suggest that they would follow the customs of that area as it is today.
