The Cogmed Platform is built around the Single sign-on concept that keeps your user logged in automatically until you explicitly use the log out functionality to log out. This means you always will be redirected to either Cogmed Coaching Center or the Training client when navigating to https://app.cogmed.com/ preventing two users to be logged in at the same time, from the same browser.
You can circumvent this behaviour by using by:
Log in from two separate Internet Browsers (i.e. Microsoft Edge for one user and Google Chrome for the other).
Have one user employ their Internet Browser’s private browsing feature to log in (e.g using the Google Chrome “incognito window” or equivalent when logging in).