Why are my two shih tzus so stubborn?

My older shih tzu Danny, whose 3-4 years old is cute, however, stubborn and often aggressive. He never listens and is always fighting my youngest shih tzu Mitch whose 1 year old. Mitch always chews pens and tips bins over, and when I tell him off by saying "No," and pull him away, he growls at me. Also he looks very retarded, he has a wonky eye, and his bottom teeth protrude over his top lip.