Welcome to our forum. It is really difficult to know what has gone on in your bustling household that has changed the balance for the kitties. In a multi-cat household, there is always the alpha cat -- the head honcho of the brood. You did get your kitty way too early, but now that he is 4 years old, he should have long settled in. IF this is new behavior, the first thing I would do is take him to the vet to have him checked out and explain the situation to them and see if they have any recommendations. A cat who goes for the jugular is trying to basically kill the cat. Bite into that vein and the cat bleeds to death rapidly. Thus you need to stop that type of aggression.
You can see if jackson Galaxy's Spirit Essences might help:
http://www.spiritessences.com. These are holistic products that you add to food or water that may or may not affect the behavior of a cat. Some people swear by the products, others claim they made no difference.
Outside of that, make sure each cat has its own territory in your home. Multiple cat trees, 6 litter boxes, multiple feeding stations (hopefully, they don't all eat out of the same bowl). Human interaction is required for bengals. They need more attention and stimulation than your normal cat. So play with the bengal and wear him out. You try different things to see if it helps the situation. You want to make sure your other cats do not lose their confidence by being attacked and bullied. That will lead to behavioral issues that you do not want to have. If everything fails, then you may simply have to find a new home for him. That should always be a last resort, but the balance in the household needs to be on an even keel. Stress is never good for humans or the kitties.
Good luck and keep us posted.