Hi @bgstaal, what a great project!
If you are still interested in using multipke Kinect v2 with skeletal tracking, you might be interested in an app that I made.
It uses Kinects on separate machines, connected to a server that governs them. The server can perform calibration (so that there is a uniform coordinate system between the kinects), filtering, body data separation etc.
The framerate of the live stream greatly depends on whether you use wifi, 100 mbps ethernet or gigabit ethernet. If you are only interested in the skeletons and body point clouds the streaming is very fast.
You can find its source and a link to binaries here:
https://github.com/MarekKowalski/LiveScan3D
And a video showing how it works here: