I bet they are playing. I guarantee you Zuzu would not go back for more if she was being attacked. You would see scratches (with blood) on the nose and throughout the head area. Sweet Pea attacks Puddles and leave scratches the rare time she has access to her. I keep them separated pretty much all the time unless I can watch Puddles very closely.
Jasper and Sweet Pea play very rough all the time. There is hisses and growls from Sweet Pea if she ends up on the bottom, but as soon as Jasper turns his back, she's on him.
. Growling and hissing is not always present when cats are playing, Sweet Pea is my first. Jasper is always the instigator because he is the one that wants to play.
Fighting cats will leave a lot
of fur behind and they will be fluffed. There will be growling going on after they are separated. It would be very difficult for you to get in between them and would probably get injured from their claws.
My recommendation: Let them be. If there is one that is really suffering, then break them up with a hand clap, then some time out.