Can we use Apple Remote Desktop to hold internal meetings screen to screen over LAN ? Like Join.me

Can you do it?

Yes. It's a bit sketchy to do this using ARD, but you can. There is one massive caveat, however. You will need a license for every client you wish to install ARD on.

From the ARD License Agreement

(i) to download, install, use and run for personal, non-commercial use, one (1) copy of the Apple Software directly on each Apple-branded computer running OS X (“Mac Computer”) that you own or control; and

(ii) if you are a commercial enterprise or educational institution, to download, install, use and run one (1) copy of the Apple Software for use either: (a) by a single individual on each of the Mac Computer(s) that you own or control, or (b) by multiple individuals on a single shared Mac Computer that you own or control. For example, a single employee may use the Apple Software on both the employee’s desktop Mac Computer and laptop Mac Computer, or multiple students may serially use the Apple Software on a single Mac Computer located at a resource center or library.

This can get quite expensive especially when the ARD software is $79 per install.
That, and it's overkill. You really don't want to give users admin level tools to just share a screen with a group for a meeting.

When I worked in the edu space, one of the products we used was Splashtop. It allowed folks to share their screens from either Mac or Windows machines. It was designed to do specifically what you are requesting - allow users to share their screens. We had an enterprise license but I believe the license for each user is under $20

What about using Mac OS Messages app with Bonjour active to discover the local users?