Thank you everyone! They did make the Berlin flight which left early and arrived early, giving them a two hour window. They downloaded the MP app and here is the text I just got:
"OMG - we breezed thru customs!! Only 2 people in line!
I can't believe more people don't use that app!, Thank you, Thank you, Thank you!!"
So all's well that ends well. I was happy to seriously decimate my SM account for the grandson's high school graduation present. I even sprung for Comfort PLus. And yes, they damn well better get their butts home for Thanksging AND Christmas this year!
Thanks again everyone. I just wanted everything to be perfect for their first trip abroad and after the troubled start to the trip, I was kicking myself for booking a tight connection. Merci!