This is the kind of situation that would stress me out instantly.
They called multiple times, both airlines said everything was fine, app wouldn’t let them pick seats or check in… and still nobody flagged anything.
Then they get to the airport and are basically told “yeah the flight is overbooked, maybe you’ll get on if someone doesn’t show.”
Traveling with a baby too… that’s rough.
They did eventually get rebooked, but two days later. That’s a huge disruption, especially when you thought everything was confirmed.
The seat selection / check-in issue seems like a big warning sign in hindsight.