In my experience, parachromis are among the most aggressive cichlids and are particulary aggressive towards other parachromis. I would not advise mixing them in a small tank, especially one with such light stocking. (no others to spread aggression)
As for the arowana, it really depends on your dovii pairs attitude. I can see some dovii living with arowna others not tolerating them at all. Cichlids generally ignore arowana, but a pair of dovii will most likely attack anything in the tank.
Tankmates I'd suggest for a dovii pair:
hardy catfish (small plecos, raphael, etc...NO north aerican catfish)
polypterids
barbs, large tetra/danio
silver dollars
maybe convicts
I'd say try it minus the managuense, you may luck out. Make sure you have a tank on hand and watch them closely, chances are if a fight breaks out the arowana will not recover. Best of luck!