I wonder if there is a way to configure a mini-van (or car), so that 2
children can sleep safely in it laying down. The kids are 6 + 8 years old.

What is the device or set-up? How does it work? If it existis: Where
can I purchase it?

If that is not possible: are there cars or minivans with reclining
seats that allow the kids to sleep in a backwards reclining position
while strapped into a booster seat? Is that safe? What car make does
offer such reclining seats?

We are currently driving a Ford Aerostar, but will buy a new van or
car soon. The kids being able to sleep safely and comfortably in the
car is a key consideration for the puchase.