https://www.oneworld.com/airport-lounges says:
Emerald and Sapphire members may invite one guest to join them in the lounge. The guest must also be travelling on a flight operated and marketed by a oneworld carrier. You must be prepared to show your boarding pass and frequent flyer membership card, with oneworld Emerald or Sapphire tier status, to access a lounge. Access is available on the day of travel (or before 06:00am the following day), at the airport from which the oneworld flight on which the eligible customer is travelling departs.
First Class passengers may invite one guest to join them in the lounge. The guest must also be travelling on a flight operated and marketed by a oneworld airline. Access is available on the day of travel (or before 06:00am the following day), at the airport from which the oneworld flight on which the eligible customer is travelling departs.
Who is the "eligible customer" here? Is it the Emerald/Sapphire/First passenger? Or the guest?
It also says:
Connecting between oneworld marketed and operated flights: First and Business Class customers connecting on the same day of travel, or before 06:00am the following day, can access the lounge when travelling between an international long haul (a oneworld international long haul flight is defined as an international flight marketed and operated by any oneworld carrier with a scheduled flight time longer than 5 hours) and an international short haul or domestic flight (and vice-versa).
Lounge access will be determined on the international long haul ticketed flight (either First of Business Class) regardless of the ticketed class of travel on the international short haul or domestic flight. You must be prepared to show your boarding pass or itinerary showing travel in First or Business class on the international long haul flight, in order to access the lounge before your international short haul or domestic flight.
What is this trying to say? Firsts can only guest someone at their origin aiport, not a transit airport?