Instead of using lemons, you may substitute oranges or a combination of citrus.
Heat oven to 375 degrees. Under cold running water, wash chickens inside and out; pat dry with a paper towel. Generously season inside and out with salt and pepper.
Roughly chop two sprigs rosemary. In a medium bowl, mix together honey, butter, chopped rosemary, lemon juice, and lemon zest. Set aside.
Combine lemon halves, remaining four sprigs rosemary, garlic, and onion; divide among four birds, and fill cavities. Using a pastry brush, coat outside of birds with lemon-honey glaze. Place birds in a large roasting pan on rack positioned in the middle of the oven. Baste every 15 minutes, and brush with any remaining glaze. Roast until an instant-read thermometer inserted into the deepest part of the breast registers 180 degrees.and juices run clear when pierced with a knife, about 1 hour. Serve hot or at room temperature.