Temperature Check The best way to determine if poultry is fully cooked is to use an instant-read thermometer. The internal temperature should register 165°F for a whole chicken. (To check, insert the thermometer into the thickest part of the thigh.)
Position oven rack in lower third of oven; preheat to 350°F. Coat a large roasting pan with cooking spray.
To prepare chickens: Zest lemons, then cut in half. Combine lemon zest, parsley, thyme, rosemary, garlic, oil, salt and pepper in a food processor or blender; process until finely chopped. Reserve 1/4 cup of the mixture, covered, in the refrigerator for the gravy.
Place chicken hearts, necks and gizzards in the prepared pan (reserve livers for another use). Remove excess fat from chickens. Dry insides with a paper towel. With your fingers, loosen skin over breasts and thighs to make pockets, being careful not to tear the skin.
Spread 1/4 cup herb mixture in the pan; place the chickens on top, at least 1 inch apart. Rub 1 tablespoon herb mixture into each cavity; spread remaining mixture under skin. Place 2 lemon halves in each cavity. Tuck wings behind the back and tie legs together.
Roast the chickens for 20 minutes. Drizzle with 1/4 cup broth and roast for 40 minutes more, basting with pan drippings every 20 minutes. Tent the chickens with aluminum foil and continue roasting for 30 minutes, or until an instant-read thermometer inserted into the thickest part of the thigh, away from the bone, registers 180°F and the cavity juices run clear.
To prepare gravy: Transfer the chickens to a platter; tent with foil. Pour pan juices into a bowl, leaving giblets in the pan. Chill juices in the freezer for 10 minutes. Meanwhile, add wine and remaining broth to the pan; bring to a boil over medium heat, scraping up any browned bits. Add any juices accumulated on the platter.
Skim fat from the chilled juices. Add juices to the pan; return to a boil, then strain into a saucepan. Bring to a simmer. Whisk in cornstarch mixture. Simmer, stirring, until slightly thickened, about 1 minute. Stir in reserved herb mixture. Season with pepper.
Carve the chickens, discarding skin. Serve with the gravy.