How To Give Each User Separate Applications Folder
It is easy. 

If you download an app from the AppStore, the app will be installed in the /Applications folder by default, if you want to hide it from others, just move it to /Users/someone/Applications/ (which is your own or another users' application folder). 

If the app is from a DMG file, just put it into your own (or other user's) 
 Applications folder, and do not put it into /Applications folder.

The application would then appear only in someone's Launchpad.