In order to clarify how one can locate and extract the engines embedded in Chessbase Online for Android, here are some screenshots. All bundled engines are available elsewhere. So, only Fritz 14 needs special procedure as described below.
1. Copy the apk to your PC
2. Open the apk as an archive using 7zip
3. Go to lib folder, then choose armeabi or armeabi7 depending on what version you need
4. Select the engine file and extract it to a folder that you can access within Chess for Android later on.
5. Install it as a new UCI engine (You can rename before installing it if you want)
6. After above steps done, in case you have installed Chessbase, you can uninstall it and enjoy a clean engines list in Chess for Android.