What are these nymphs doing?

[Koen G]

The three nymphs on the left form a similar group to the three at the bottom. I have no idea of what they might be doing, though.

Yes, I think they may represent different "scenes" or "steps". Though it's not clear at all if and how they can be divided.
I've studied other manuscripts where scenes are presented simultaneously without borders, and there the most effective way of telling whether a character is repeated is by their robes. That's quite the problem in Q13

One way of going about it is to assume that the paired nymphs represent different scenes in a story, or different steps in a physical therapy (to follow VViews line of thinking). 
If they are wrestling, it would be natural to see the idle nymph as a referee - but she's missing for one of the pairs so this is problematic.

There's something strange though: a clear pen line in the water; what could it be?