Moving hives can be quite tricky, and it would really help you if an experienced beekeeper could assist you. Not essential, but much easier if that was possible.
Definitely move them together, unless you are going to remove the super for winter. I think @JeffH and @Peter48 are quite a way north of you, but I know they have nectar flows just about all year. If that also applies to your region, you would leave the super on for the move.
The usual method is to strap the boxes together very securely with hive straps or a ratcheting strap. The strap should go under the bottom board (on the outside, of course) and over the roof. I think @JeffH has a nice trick for wedging the wood frames inside the hive box, so that they don’t swing about when you are driving, crushing bees. You would want to do the wedging in daylight, the day before moving. That will give the flying bees a chance to settle down before you close up the entrance.
You can close up the entrance with some dense foam rubber or staple insect screen material over it for ventilation. Many people also change the roof for one with ventilation in it, as the hive will be full of bees, all trapped inside during the day. This helps prevent them from overheating. Position the hive in the vehicle so that the frames align front to back and take corners very slowly and gently. That alignment will protect them from braking and accelerating, but not cornering.
The hive will be heavy, so be ready to lift up to 70kg depending on how full it is right now. I have moved hives that took 3 people to do it safely, because of the weight.
Good luck, and let us know how it goes.