2 Apple IDs on one device?
Yes, you can have apps installed from different Apple Id's.  Simply log in with whatever account you both want to use for purchasing.  You can log out and back in with a different App Store account at any time.  

I have multiple accounts, and multiple devices sharing applications.

To follow up the other responses, your App Store account can be separate from your iCloud, Messages, and FaceTime accounts.  I use a separate account (Apple ID) for iTunes purchases than my iCloud account. 

Some people even split things the opposite way - sharing email, FaceTime and messages but having different store accounts. It's really up to whatever works best for you and your devices.