Although Thais are always on a first name basis because they eschew the use of last names, they almost never use the person’s first name or nickname on its own. They almost always add some kind of honorific or relationship title.

Younger sibling [or younger friend]: น้อง /nóng [in this novel, written as Nong]
Older sibling [or older friend]: พี่ /pêe [in this novel, written as Phi]
Mr/Miss/Ms/Mrs/: คุณ /kun [in this novel, written as Khun]

(Source: expatden.com)

Thai names follow the Western European pattern of a given name followed by a family name. […] Thai names (given and family) are diverse and often long. […] Additionally, while given names are used for official purposes and record-keeping, most Thais are also given a nickname at birth which they use in their daily life, including at school and in the workplace. In many social situations, the nickname takes precedence over the real name.

(Source: wikipedia.com)

 

One – Lamon Saengsuwan
Keb – Chatchom Sichantha
Ford – Summatra Chanthangam
Moon – Mekhala Kawatkul
Khem – Khemkhaeng Wongsarot
(listed by age, oldest first)

Note: Keb and Ford are the same age.