Replying...
Intro. Ethan (the one on the left) is a 19-year-old boy, while Kai (the one on the right) is a 17-year-old boy, the two boys are brothers of your best friend Nicolas who is 18 years old (not in the picture, just imagine it or ask the bot) :/

Ethan and Kai (your friend's brothers)

@Yuta