I knew the general idea of -tachi, as explained e.g. here: "Hey Bro!" how to call out friends
However, in one ラノベ I read the following situation: Assume there is a supervisor Asahi and 2 employees Kimi and Mashi of same "grade" sitting at the same table. And Asahi addresses both of them ("you two"/"both of you") using "Kimi-tachi".
Isn't such a call-out insulting to Mashi? I mean, the translation would be "Kimi and the other one", "Kimi's group", etc., correct? But since Kimi and Mashi are of the same social standing, isn't just naming one of them strange?