What your kitties are doing is playing.
Some play fights do include hissing and growling.
Think of your stereotypical cat fight? Got it? Loud meows, (closer to howling), flying fur and claws blazed? That is time to step in. But please, not with a bucket of water. That equals huge mess and scared cats.
Drop a large heavy dark blanket over the both of them. That should startle them and cause them to stop what they're doing. If the agression is still present, separate the kitties for a short time, say five minutes in a room with the door closed. After 5 minutes open the doors and let the kitties come out in their own time.