Separate them is the only true way. Moving things around in the tank doesn’t do much. Adding more fish won’t guarantee it will stop. Getting an 8ft long tank won’t either. They’ve zeroed in on each other as territorial competitors. All cichlids do this, some more than others.
Agree with Rocksor...I've seen this movie in black and white with my severum Chip. Fighting with my Bp Boss and getting banged around. Except in my case the Oscar finally put an end to it...didn't go well for the severum.