Migrate multiple Craft 2 CMS sites on cPanel
Have you checked the permissions on the sever? As 500 usually comes due to server permissions or due to wrong .htaccess or wrong Rewrite file. Have a look at .htaccess file. 
And make sure to check your server error logs, they might provide you some valuable input for the errors. 

If you find some specific errors, please share them so the community could help you better.