In general it is not possible to have multiple Mobile Authenticator apps generating valid codes at the same time for a given user. Every time you activate a user, a new QR code (and hence a new secret key) is generated and the last key will override all the previous ones. Therefore, only the last Mobile Authenticator app that you have activated, will generate valid codes for that user. The other apps will generate invalid codes, which will be rejected upon login.
There are few Password Manager and Mobile Authenticator apps (like 1Password, Authy) which can sync the codes across devices (through the creation of an account on their platform). In this way, they allow multiple devices to display valid codes.