I don't know why they can't come home one day early if the OP's husband is so desperately important. If he needs to fly business class why can't he fly business class on his own on the way back? The husband dies sound like hard work but surely he is less likely to need the OP than their children . We are not talking about a few hours , this is a long haul flight.
I have no issue with holiday clubs, I have always used them with our children so they can be with other people their own age. We use the time to read or have sex, usually the latter. But thee is a difference between organising something your children would enjoy and deciding to exclude your children from something. I never see holiday clubs as time to get away from my children, rather a chance for them to get away from me.
I can not imagine serving my children different food at home , so my husband and I sitting down to fillet steal while they have chicken nuggets. Of course I have things my children do not have but that is different to sitting your child down and giving the an inferior version whilst you have the better version.
The back seat/ front seat in a car is totally irrelevant because you are not involving anyone else in the equation. There are not another 100 people in your car who have paid a hefty price for their ticket and are also trying to enjoy their holiday.
My children are usually well behaved however I would not assume they would be perfectly behaved for 10 or so whilst in a restricted rather false environment. It is only on MN that you " meet" people who think their children are perfect and anyone else is incredibly lucky to breathe the same air as them.