Foolish decision on your part
The couple was not intelligent enough to seek out and then obey the rules. They whine and bitch and moan because they chose not to do the necessary planning and tried to bully their way through because they were Americans.
The cheapest fares turned out to be very expensive
At the very least, Swiss Air should have checked their documentation before departing the US for Switzerland. This is on Swiss Air in my opinion.
And personally, I don’t think Swiss Air should sell tickets to Americans if the flight passes through territory that Americans are not allowed to enter.
I’d agree with you if this couple were specifically buying tickets to Switzerland. But they weren’t. They were buying tickets to Greece. Swiss Air should not have been allowed to sell them these tickets.