I am sorry to hear about the behavior problems that you have been having.
Here is a link to a great site with lot s of ideas about dominance and aggression behavior in cats:
I have found that some combination of keeping them separate, and using positive (food) rewards as well as dissuader (I like the sprays of water approach) is the best approach.
If the problem gets too bad, some medications that your veterinarian can prescribe might become necessary!
I hope this helps!
As always, if you have further questions or concerns, please don't hesitate to ask them using the "reply" function!