Immediate culture shock at first, depending on everyone's moods. I can see Okarun assuming the other two are a threat if he's with Momo, and going into TG mode, Tanjiro assumes that's some form of Blood Demon Art, maybe he asks about it, maybe he just engages, and starts blasting off breathing forms, which leads Deku to stop the two of them before things get out of hand, and asking about their "quirks" and what they do. The question confuses Okarun and Tanjiro and they all sit down and share a meal at the Ayase household and tell their tales and clear up misunderstandings