It looks like you copied a single host file to all your VMs. The DS2Web and OlioWeb VMs are setup to require a specific host entry for each VM.
Each of your DS2Web VMs need a DS2-DB entry in their hosts file with the IP of that tiles DS2DB VM.
Each of you OlioWeb VMs need a OLIO-DB entry in their hosts file with the IP of that tiles OlioDB VM.