It's very interesting that Kyouka gets very jealous when women outside her unit get close to Yuuki but when it comes to her own unit, she practically encourages it. She doesn't seem to mind at all when Shu Shu or Himari do anything with Yuuki.
Even just interacting with the family they should have learned a bit, especially the daughter. I have lived in places with differing languages and you learn the basics after a while.