I would not take them to the off leash park until they are ready. The rules for off leash parks are that you have voice control over your dog(s) and so at this point they are probably not ready (or, Bruno is not ready but Ares might be allowed to have the privelege?)
Not being able to bite isn't going to stop the aggressive behaviour, it will, however, at least stop him from being able to injure someone by biting them. You could try a long line (long leash that is 20-30' long) to give him some ability to run and play, but still allow you to control him.
Also, pulling on the leashes and making them taut when the dogs are are being aggressive to others can actually cause more aggression. Instead of pulling on the leash, put yourself in front of the dog and demand his attention, if you were not able to distract him before he gets to that point.
Good luck working with both of them!
It'll be worth it when you can take them to the offleash park and watch them play nicely with dogs of all sizes!