Right now two people, (1) and (2) have a booked round-trip itinerary from A → B → A.
I am hoping to add a stop to person (1)'s travels, and not to person (2)'s. (1) would travel from A → X → B → A and (2) would travel from A → B → A. (2) would travel on the already booked round-trip flight.
What would be the best (cheapest) way to add a stop to an existing reservation for one passenger and not the other?
Secondarily, is there a way to not change the existing round-trip reservation (as to avoid United's $200 change fee) and to retain return leg for (1)? In this scenario, (1) would not be flying from A → B, only the second leg, from B → A. (2), however, would fly the whole round-trip.
Alternatively, is there a way to avoid United's change fees if I booked the A → X → B itinerary with them? (I would be booking two more flights with them; maybe they would waive the fees?)