Play store apps - How does it work for multiple accounts?

This has been so confusing to me. Please help.

OGA - Old Google Account. Used it in my old Nexus 7. Installed some apps on it.

NGA - New Google Account. Added it to my Nexus 5. Installed/Purchased new apps.

Now, I added OGA in my Nexus 5 to enable GMail access on the phone. But as soon as I added the account, it installed all the apps from OGA on my Nexus 5. I don't want to do this. I only want emails of OGA on my Nexus 5. I don't want apps from OGA to be installed on my Nexus 5. How do I do this?