Originally Posted by
cre95
They should be able to upgrade one leg only after splitting the two passengers into their own PNR. Before doing that, you could get a sense of the pricing by doing a test booking for 2 passengers while selecting the desired cabin for each leg. If the delta in price is not attractive, they may just want to leave the booking alone and keep everyone in the same PNR rather than splitting across two records and increase potential bumps during IRROPs
To be clear, you can generally upfare each one-way direction (if you have a connecting itin, both legs are generally on the same fare in the same direction and thus you will be upgrading both legs when you do an upfare) separately from each other. For international fares, this generally does not require repricing the one where there is no change. For DL domestic fares, fare rules specify re-pricing entire trip in both directions based on current fares (even if you remain in same cabin in one direction of travel).