You know me, I love these guys. So yeah, we're doing them next, although there's much less to say, but I still find it quite interesting.
The only person who calls Kid by his name, with no honorifics, is Killer - and Kid does the same for him. This shows they treat each other as equals.
Keep in mind that the name Kid is originally pronounced "Kiddo" in Japanese, and Killer is "Kira".
Heat refers to Kid as boss or master ("okashira"), whereas Wire calls him captain ("sencho"). Kid seems to call them by their name, although there is only one instance when Kid mentions Heat name, or better, "Heat and the others".
Killer is Killer-san for the crew, which shows that they recognize and respect his authority.
...also, if you're curious to know, birdie would initially refer to them as "Eustass" and "Massacre Soldier" ("Satsuriku Bujin"), but later change to their first names, without ever using honorifics (obviously -.-).
The nickname "birdie" would sound like "bādī", while "kitty" would be translated in "koneko".
