So, you have two guests that you want them to communicate with the Internal network? Is that what you're trying to do?
From the log you attached, I see that you have an Ubuntu based OS, but you have the Ubuntu fork of VirtualBox:
VirtualBox VM 5.0.40_Ubuntu r115130 linux.amd64 (Nov 6 2017 17:41:59) release log
You can either ask in their forums for help, or completely remove/uninstall/delete/purge their version and install the official version from the Downloads section of VirtualBox (
https://www.virtualbox.org/wiki/Downloads).
Your VMs will be unharmed.
00:00:00.134971 [/Devices/e1000/0/LUN#0/] (level 4)
00:00:00.134972 Driver <string> = "NAT" (cb=4)
You also have 1 network card (NIC) and that is using the "NAT" mode, not the "Internal".
Could you please describe in detail what you want to do with your VMs? The end-goal, not what you think the solution should be...
BUT... you need to install the official version of VirtualBox first, before we continue this discussion.