It seems there were 2 copies of this thread but one of them disappeared (was removed?). I posted in the other one, I think, but will now post here instead.
Op, I'm so sorry this has happened. I took it as your dd asked you this last minute and was mad when you said no. But now, BlueBelle has me wondering, did you promise to drive them and then change your mind last minute? That would change the picture a bit. I still feel for you though.
Also, how old are your gc? That might make a difference. Unless they are teenagers, they may have been voicing their parents' feelings more than their own.
No matter what, those messages were unfair, as you say, imo. Again, so sorry. Even if you changed your mind last minute, they could have easily gone the next day surely, just as you were planning to do. It shouldn't have been such a big deal.
It was also very unfair, I feel, to accuse you of "starting a row." You did NOT. Dd and sil did NOT have to fight over this. That's THEIR doing.
Maybe there's an underlying problem of dd not driving or not driving long distances or at night? She may have to change that or accept that she can't expect others to drive her where she wants, when she wants all the time. But you can't do anything about this, of course.
Maybe they were just all reacting in the moment. I hope you all ended up going on holiday, anyhow, and that all had a good time.