The morning before roasting, spatchcock one of the turkeys. Remove the backbone by cutting 1 1/2 inches to the left and right of the backbone (opposite side of breast) from front to back. Remove the backbone and reserve for stock if desired. Place the turkey breast-side up on a large flat surface. Place a clean kitchen towel on top and press down firmly on the breast to flatten. Season both sides of the spatchcocked turkey with 1 tablespoon each of the celery salt, granulated garlic, granulated onion and pepper.
Season the whole turkey inside and out with 1 tablespoon black pepper and the remaining celery salt, granulated garlic and granulated onion. Allow both turkeys to sit in the refrigerator overnight, uncovered, to dry the skin.
The next day, allow the turkeys to come to room temperature for 1 1/2 hours.
Arrange one oven rack in the bottom lowest position of the oven and one in the top third. Preheat the oven to 400 degrees F.
Combine the minced parsley, tarragon, oregano, minced thyme, lemon zest and shallots with some salt and pepper in a small bowl. The salt will help to draw the moisture and flavor from the mixture. Add the olive oil to form a paste. Divide the mixture between the turkeys and spread all around both sides of each turkey. Season again with salt and pepper. Halve 3 of the lemons. Stuff the cavity of the whole turkey with the lemon halves and parsley and thyme sprigs.
Divide the carrots, onions and fennel between 2 roasting pans or baking sheets. Arrange the spatchcocked turkey skin-side up on the vegetables in one pan. Put the whole turkey breast-side up on the vegetables in the second pan. Divide the stock and wine between the 2 pans.
Put the whole turkey on the bottom oven rack and the spatchcocked turkey on the top rack and roast, basting every 30 minutes with the pan juices and adding a little more liquid to the bottom of the pans as needed to prevent burning. Keep an eye on the turkeys: when the spatchcocked turkey is nicely browned, remove the roasting pan and carefully move the top oven rack to the middle position (see Cook's Note). Move the whole turkey to the middle rack and the spatchcocked turkey to the bottom rack and continue to roast until the thickest part of the thighs registers 155 degrees F on an instant-read thermometer, about 2 hours total (10 minutes per pound) for a 12-pound spatchcocked turkey and 2 hours 25 minutes to 3 hours total (12 to 15 minutes per pound) for a 12-pound whole turkey. Allow the turkeys to rest for at least 1 hour before serving.
If you don't want to move the hot oven rack once the spatchcocked turkey is nicely browned, just cover the spatchcocked turkey with foil for the remainder of the roasting time.