CAN I DIVIDE LAN?

If you're using Windows as the desktop OS, and not using a domain server, you just need set up two workgroups and decide which computers go in which group.

Right-click "My Computer", select "Computer Name", select "Change Workgroup" and type in the name of the workgroup you want. "WG1" and "WG2", or whatever you're using.

The computers in WG1 will be able to see each other, but not the computers in WG2 directly.

However, in a Windows environment without a domain server, if anyone clicks on "See Whole Network", they will be able to see the other workgroup. You need to disable that option (can be done from an Admin account in your account manager).

Both of these actions, setting the workgroup and disabling "Whole Network", will need to be done one-by-one on each computer. There might be a way to automate it, but I'm not familiar with such and I don't think there is.

If you have a domain server, it's a whole different game to do this. From your post, I assume you don't. If you do, it's a lot easier to set up multiple domains and manage the rights workstations and users have from a central point.

In either case, all the computers on the LAN should be able to get their internet connection from your router, regardless of workgroup.