That does sound a bit like Zev and Kai.
I think, as long as they're not really aggressively fighting ie arched back, all fur on end, lots of teeth and claws, and drawing noticeable amounts of blood, it's probably OK.
I'd guess it's a combination of trying to sort out their hierarchy, and also that kittens do play fight a lot.
Kai's a lot older than Zev, but he will join in sometimes, on other occasions he just ignores her, aside from the odd swipe of a paw to warn her off. What used to fascinate Zev, was Kai's big fluffy tail, which he would of course start twitching when she was annoying him, and which just encouraged her to attack it! She's not quite so bad with that now.