I am sorry no one has responded to you in so long.

You could us the Ultimate Member plugin and the P2 Theme to accomplish this.

Here is a tutorial to setup the P2 theme as an Internal Communication System.
https://www.wpbeginner.com/wp-tutorials/how-to-make-an-internal-communication-system-in-wordpress-using-p2/

Best of Luck and I Hope This Helps You!

~Josh