You can create the environment set up as follows
You will need to have atleast 3 Vlans in the real world ,so that the VMs can communicate with each other. Also you will need a virtual router appliance. You can use monowall router, which is available for download as an appliance from here : http://m0n0.ch/wall/downloads.php
For each monowall, there is a Lan and Wan interface. In your case you can use the the IP ranges 10.0.1.x,10.0.2.x & 10.0.3.x for this. The Wan ip range will correspond to your 3 vlans in real world, ie the network in which your ESXi servers are connected. Since there is only one NIC card in the servers, you will hve to enable trunk port on it to allow the 3 Vlans
Please have a read thru the monowall documentation. You will need to set up a NAT to map your Lan network to the external Vlan IPs. Also you can configure the firewall in it to restric the traffic between the networks, thereby simulating the real environment. Do give it a trial and get back if any help is required