Could you explain how you came to this conclusion? Granted, none of them specifically acknowledged that they did know of them, but I'm fairly certain none of them reacted to the term "Power Rangers" in such a way that would indicate that they didn't. I think I would have remembered that. Though it's possible something is slipping my mind.
One of them asked "Who are those?" in reference to all the Ranger figurines along the walls. Gosei specifically had to explain to them what Power Rangers were.