It kinda depends if Isabelle’s dad is on the birth certificate If he is then he also has parental responsibility, so he could cause shit
In any normal persons situation they would just go and if the dad is a no show then he’d never know as he’s not around anyways ,
They advertise and show off with their trips ,
Maybe they went to court and got permission or something no judge would stop a kid having a holiday when there is no risk of abduction, but there was problems before with the ex .
Ps I don’t have kids and I’m certainly no expert apart from google law sites