So here's one.. . Both passengers are Male, so the names on the manifest would seem OK., I cant imagine the crew sees the AGES? ... Let the pax ticketed in Y class, take the J at the beginning of the flight. I have never heard of a flight crew ever asking for an ID on the airplane. 8 hours in, have the passengers swap. If the crew says something, you can show them the boarding pass, and tell them you realized you were in the incorrect seat, so you wanted to go back to your assigned seat. What could the flight attended do. Tell you to go back to the seat that is incorrect?