Rinse the chickens inside and out under cold water, and pat dry. Truss the legs with kitchen twine, and set aside.
Heat a charcoal or gas grill. If using a charcoal grill, arrange the hot coals around the inside edge of grill. Arrange the chickens, breast sides up, in a row across the center. If using a gas grill, cook the chickens over medium heat until brown on all sides, rotating every 5 to 7 minutes; cover the grill as needed to maintain heat.
Baste the chickens with barbecue sauce. Continue cooking, basting frequently, until an instantread thermometer registers 170F in the breast and 180F in the thickest part of the thigh (avoiding bone), about 1 hour. If the chickens brown too quickly before they are cooked through, transfer to baking pans and finish in a 350F oven.