@prem-ranjan ,
You would connect them together using virtual networks. But I think you might run into a little bit of a resource issue with your proposed setup.
RAM
You have 16GB of RAM and are giving the two Server 2012 machines 10GB. That only leaves 6GB RAM for the other four VMs and the laptop itself. Windows 10 likes 4GB but you can get away with a little less, it will affect performance. Ideally each of the VMs would need 4GB RAM. The SQL server will need more depending on the databases.
Hard Drive
Do you have an HDD (spinning disk) or SSD? Disk contention is going to be a real problem. On a 7200 rpm HDD, I usually saw significant performance issues once I started the third VM. To run six VMs, I would recommend an SSD for your laptop OS, and a separate SSD for your VMs. With this setup, I have successfully ran five VMs simultaneously. You could put one or two VMs on the OS drive if necessary.
Processor
You didn't say what processor you have. When you say "old dell laptop", how old are we talking? Hopefully at least an I5 or similar.
Networking
I am assuming most of the lab networking will be between VMs, so the WiFi should be fine. Just don't try to run Windows Updates on all of the VMs at the same time, you will be stuck for a while 
Seems bad, but all is not lost. You can do things to make your setup work. Most likely you don't need to have all six machines running at the same time. Just start the ones you need for a particular exercise.
Hope this helps, ask more questions if you need!
Mike Rodrick
Edutainer, ITProTV
**if the post above has answered the question, please mark the topic as solved.
