Does someone have experience from this?

If I book a RTW for two people travelling together they will end up on the same PNR as far as I understand. If I after ticketing want to change travel dates for one of the persons, will they charge me? Technically, it's only a date change which I am not supposed to have to pay for. On the other hand, since they will have to split it into two PNR's I'm assuming they will have to re-write one of the tickets. So, do I pay the change fee or not?