Preheat oven 400F.
Pat the outside of both turkeys with paper towels until they are relatively dry. Stuff the cavities of both birds with the onions, carrots and celery. Place 2 bay leaves and 5-6 sprigs of thyme in each bird.
Season the outside of the birds with the grill and poultry seasonings, and some salt and pepper. Rub the outside of each turkey with the soft butter and then place in a large roasting pan. Tie the ends of the legs together with trussing string.
Transfer turkeys to the oven and roast until meat thermometer reads 160F, about 2 1/2 hours. Remove from the oven and let the turkeys rest loosely covered with foil for at least 20 minutes.