No, that is not possible. A smartphone can only be registered once as a MobileTAN push device. Every user needs his/her own smartphone to install the BusinessNet app and for registering the device as a user of BusinessNet.
Yes, further devices can be used as an additional device. The additional device provides all information and details, and orders can be set up and saved. But orders are only approved on the principal device.
BusinessNet is accessed only via the TAN method; parallel use of MobileTAN SMS and MobileTAN push is not possible for BusinessNet. It suffices if you install the BusinessNet app once and activate MobileTAN push for any BusinessNet access. This activation automatically covers all other BusinessNet access methods.
You have to install the MobileBanking app for 24You and the BusinessNet app for BusinessNet on your smartphone. The TANs for BusinessNet and for 24You can be obtained in the respective app. You can use both apps in parallel on a smartphone.
You have to install the BusinessNet app on the new device and register the new device as a new MobileTAN push device. You will then receive another TAN on your old device as evidence for the switch to a new smartphone. This TAN has to be entered in your new smartphone to conclude the activation process.