You need to stay on top of both of them and be consistent. Shadow the boys and see what triggers them. If they are fighting over a toy, stop them before it gets physical and take the toy away so that no one gets to play with it. Explain to them that if they continue to fight over toys then you will take them away and no one gets to play with them. If you cant keep your eyes on them, then they need to be put in a playpen or a highchair so they can't bite or hit each other. They will learn that until they can play nicely, they have to be seperated.