First is to look for triggers to his biting. What is going on when he bites? It's typical around 1 because they get frustrated trying to walk/talk. For 3, he's probably getting over stimulated. It's almost like a little puppy wanting to play -- he nips at you.
If you can recognize the situations where he is prone to biting, then you can remove him from the situation before the actual bite.
When he bites, tell him "no" in a firm, strong voice. Then give ALL of your attention to his older sister. Do not give him any attention.