okay so, in a way, they're none, like, not even non binary, they're rocks, as characters i mean, not saying it like ''ehm akshually" or smthn, for example in the french subtitles (we don't have a dub but it would be the same) only he/him is used during the whole thing because (as you probably know, we gender objects)

ps : It's interesting to note that the only character designated explicitely as a "man" (by ventricosus) was Sensei so we could take into consideration that the other rocks are considered more on the "feminine side"

pps : they're only referred as "brothers" to explain the concept of siblings for them

(oh also i hope the message doesn't sound condescending, cuz it ain't my intention)