Heat to boiling, chilies, onion, seasonings, and broth. Cover & simmer until chilies are soft, about 15 minutes. Let cool, then blend in blender until smooth. Pour into bowl. Coat chickens well with sauce. Grill chickens in a barbecue with a lid by indirect heat. (About 75 briquettes around the outside of a drip pan). Place the chicken halves in the center of the grill, skin side down. Cover the barbecue and adjust the vents. Cook, turning as needed. When half done, baste again. Continue to cook until no longer pink (about 45-60 minutes). Bring remaining sauce to a boil to serve with the chicken.