1) As first step, try chrome and firefox instances running on the same computer ( you will probably need a second webcam).
2) Then try it on two computers behind the same router.
3) Then try it on two computers in different subnets.
If 1&2 work, but 3 doesn't, then you need a TURN server.
If 1 or 2 don't work, then you've got something more interesting happening.