A Renault Grand Scenic works well as a 7-seater, as the insurance isn't too bonkers and the spare seats in the boot are not right up against the rear windscreen, you still have a bit of a boot with them up.
Sometimes it makes sense to have something to give kids at strictly defined half hour intervals, so they get a sense of time and also get distracted. Half the problem is not having a clue how long they have to endure the situation, I think. Another strategy some people use is to give them a simple map and mark the route, where you are stopping and so on.
I used to prepare a little surprise travel pack for each child with drink, snack, sick bag (you can even buy little kits online with a bag and a wet wipe, or nick them off ferries/planes), magazine, little toy, colouring books and crayons, etc. All new and exciting pound shop type stuff. Everyone would routinely get a neck pillow and little blanket for a longer trip as well. Basically I would top load efforts so there was nothing left for them to ask for. I did this for plane and train trips too.
You can also get little lollipops to keep in the glovebox that car sick children can suck to take away the nausea. Travelling with an emergency hazchem kit with granules that soak up vomit/diarrhoea, gloves and an apron is a brilliant strategy and stop the car reeking, if the worst does happen, I keep spare pants, wet wipes and socks permanently in one of the storage bins under the front seats, play things are permanently kept in another one near the kids (for spontaneous restaurant outings), and another one contains my emergency car things such as spare bulbs, torch and warning triangle, so they are not at the bottom of a fully packed boot. I always have a bottle of water with a sports top stashed away, as well. I have bags tucked away for sick encrusted clothes that can go into the washing machine along with the clothes, so you don't have to empty the bag. We also have travel tissues, the most generously stocked first aid kid known to man with all sorts of tablets and potions, and a spare Radar key for DS2. My car is like mission control, tbh.
I've equipped older children variably with Walkmans, iPods, DSs and portable DVD players, which has worked well too. I keep a spare set of headphones in the car, and a splitter.
We stop every two hours and every time someone gets distressed or stiff (usually me!) I often map out nice service stations and so on beforehand. I tend towards generosity in the service station shop and cafe.
Bribery is good too. Brief them beforehand about behaviour expectations, then explain what wonderful thing will happen if they manage to keep quiet and also distract any babies nicely during the trip. Also try explaining very simply about what it's like driving and potential risks if it kicks off in the back (I managed to crash once whilst yelling at DD to shut up and stop distracting me, that certainly sobered her up fast and she was an angel after that! Not my finest hour, though). I think even with stroppy children if you actively train them to understand what is going on and what is required of them, you can improve things, but this needs to be done outside the car as well as within it.