In the past Frontier made an effort to seat people traveling together together. based on same name and/or same ticket. They would try to make accommodations at the gate. I don't know if they've changed this lately. I doubt they would bump you over failing to pay. I would however make sure you checked in as soon as possible to get a seat assignment that makes it much less likely you will be bumped in an overbooked situation.. They generally assign seats from the back to the front and a surprisingly large number of people don't bother to check in in advance.
Good luck and let us know what happens.
Last edited by rsteinmetz70112; Apr 23, 2019 at 9:52 am