First, you have to understand how to addressing in Vietnamese
Anh: mean older brother, use it when addressing a young male, less formal
Chị: mean older sister, use it when addressing a young female, less formal
Em: mean younger sibling - brother or sister, use it when addressing children, both male or female, or anybody younger than you.
Ông: mean grandfather, use it when addressing an older man, can be translated as Mr or Sir, formal, respectful
Bà: mean grandmother, use it when addressing a married woman or a woman older than you, formal, respectful
Cô: translate as Miss
Second, I will explain 1st, 2nd, and 3rd person pronouns in Vietnamese
+ 3rd
- He: anh ấy, ông ấy, chú ấy...
- She: chị ấy, bà ấy, cô ấy...
- It: nó.