In my experience, 'play' fighting is chasing each other around, some annoyed squeaks and a bit of nudging. When I've seen mine properly go at it, they've been rolling in a ball and have drawn blood. They are all separate now and doing great on their own. I think you've done the right thing.
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Sam, plus Maggie and Cas.
Pawprints on my heart: Frohike, Langly, Byers, Max, Albert and Charlie