In order to keeps things simple, you should book in Economy (V fare) the exact same itinerary you want to upgrade. Just make sure that there is enough award space so as to be able to upgrade the 3 tickets.
Edit: I thought you were looking for 3 award tickets. Same explanation applies for 1 ticket.
Last edited by Mister P.; Nov 20, 2018 at 2:51 pm
Reason: Amend explanation