I know it is not your question, but unless they actually wanted that change of date, I have exactly zero doubt that BA would have been able to offer same day itineraries, though with one stop. There are literally dozens of options from any major US airport to London every day and it is routine to reroute people.

I understand from what you say that your friends already accepted the "bad" rebooking, and technically, it is a one shot thing and once you accept any further changes are chargeable. Having said that, if it were me, I would recommend that they call BA anyway, explain that they were a bit panicked when they saw the options and since they were only given +2 or -2 tried to pick the lesser evil and that it is only after that that they realised that they should have called to ask for a same day alternative via other routings. A supervisor may be willing to make an exception and and change the trip back to a same day option at no cost (there is no guarantee that they will, but i think it is worth a try).