Boo, overreact, Inigo! But Tidus doesn't mind either way (at least he didn't say that meant Della was calling him a kid too), giving some thought for that third option.

"Hmm... don't know. That sound like anyone on the train you know, Inigo? We might have to keep applications open for the third slot." A pause, and then he turns back to Della.

"But I'm the favourite son, right?" Whisper whisper (that's totally audible). "It's okay - Inigo doesn't have to know."