If you are set on paying the entire bill, go with a travel agent or the airline group booking desk. I did exactly what you are contemplating and got burned do to dynamic pricing. The ticket prices jumped by more than $200 pp after I purchased the first six tickets. Because family members 7, 8, 9 and 10 made their decision to go based on the original price, I paid the difference.

Let them make their own arrangements, it will be less stressful for everyone. If they can't or are unwilling to do so, VG might not be a place they want to be for a vacation.