The standard answer for “do I need a visa” is often “see what Timatic says”. So I checked:

https://www.united.com/xx/xx/timatic?i=TIMATIC






For the Germany connection it shows:





Sadly that is confusing me more than the German web pages. Does this mean a TWOV is possible, but only if they have a visa from the countries listed? What if they travel to India?

Guess it’s too early here and I need more coffee.