Go to virtual box preferences, select not networks under network segment and create new NAT network.
Then go to virtual machine settings on the adapter one tab under network segment.
Attach the virtual machine to NAT Network and choose the net network you created.
So now let's provide connectivity between your virtual machines.
So the way I'm going to do this, I will include all of my virtual machines in a NAT network.
I'm first going to start with Colly, so I'll choose it.
Click settings.
Go to network settings, change NAT to Nat Network, right, and click okay.
Now do the same thing for the other virtual machines quickly.