How to group certain apps and add as a stack to the Dock?
Create a folder in your user directory.  Make an alias for each app and move the alias to the folder.  Then drag the folder down to the dock, to the right of the divider line but left of the trash.

Once the folder is in the dock, click on it and the available apps will pop out and you can select whichever one you like. 

P.S. this works for any kind of file or document, not just apps.  I.e., if there are favorite docs frequently used, you can put aliases in a folder and add the folder to the dock.