In a single engine piston (SEP) aircraft, certificated or permitted for a single pilot, then unless one of the occupants is a certificated instructor, then everyone apart from the pilot is a passenger. The pilot would normally be the person who has signed for the aircraft in the tech log. In the UK, if the pilot hasn't done 3 takeoffs and landings in the past 90 days then it is illegal to carry passengers. This transcends what the insurance company might have to say about recency checks. For unusual types, especially those on a permit, the Light Aircraft Association run an excellent scheme whereby pilots experienced on type have a Class Rating Instructor certificate, enabling them to do checkouts. Otherwise, find a friendly local instructor if it's a certificated (Cessna, Piper etc) type.
Apart from the above, I think it's an excellent idea for group members to fly together, provided it's within the law. It not only spreads the cost of a trip, but helps disseminate knowledge and increases airborne experience.
TOO