Lesson Learned: AA/AB AAdvantage Award Nightmare
Checkin mix itinerary has not been a problem (JFK-ZRH-DUS). AA was able to check in AB ZRH-DUS.
As for the short connection at TXL, if the ZRH-TXL was delayed due to reasons within AB control you might have considered casually walking over to TXL JFK flight and missing the flight and claim EC261/2004 compensation; could have been as high as €600 per passenger. LOL