Chiellini + Chiellini wouldn't work. Chiellini is an aggresive anticipating CB, he goes towards the attackers and the ball, he needs someone to cover the gaps behind him. Chiellini + Chiellini, would be like Cannavaro + Pepe, not that effective as both are of the same mold or least lack someone of a different mold to compliment them.
P.S. Giorgio does in fact have a twin brother.