I'm running HDMI-1 (HDMI obviously) and DP-1 (DisplayPort 1.2 Alt Mode on USB Type-C) simultaneously, works fine.
I have the 7" monitor for the eDP-1 (micro DP?), but haven't tried it yet. Attaches to the motherboard with an eDP adaptor.
Shows up in the X server as eDP-1 along with DP-1 and HDMI-1 as above. I can't think of any reason they would not all work at once.
- Mark