Responses
From their name. Daddy Kazuhiro, kazu literally mean number,
- Hajime meaning start, sometimes using kanji one
- Gil read as jiiru=ji=two
- Mishra=mi=three
- Roberto=roku=six
- Isaac I assume from irebun=eleven or just i=ichi=one since first already taken by Hajime only eleven left
-and this dwarf is Toko=tou=ten.
It's simple if you understand japanese lol

I know birth order is still quite important in Asia, but how the heck do they all know if a new sibling is an older brother/sister or a younger one?