Able to log in aem author instance with same user at the same time using 2 separate browsers

Short answer No. 

The AEM default login relies on tokens that are stored on the client side, that's why you can log in in 2 separate browsers with the same users at the same time.

If you need to change this behavior to allow a user to log in just once, you would have to create a custom Authentication Handler which will check if the user is already with a session open. To check if the session is opened, you can use something like this: https://www.aemtutorial.info/2021/11/generate-reports-for-users-last-log-in.html 

Fore more info check these links:

https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/how-to-create-custom-authentication-handler/m-p/238421 
https://kbwebconsult.com/authentication-handler-in-aem-custom-approach/

 https://www.aemtutorial.info/2021/11/generate-reports-for-users-last-log-in.html