I couldn't find info on removing the panels for transporting separately. But in the manual it instructs installing the feet while the speakers lay on their sides, just like most of our speakers.
So,
Try to find some anti-static/lint-free material with which to wrap the speakers.
Get some cardboard sheets so you can create a flat surface.
Lay down some moving blankets on top of the cardboard.
Lay the speakers on their sides, preferably with the woofer ends facing front of vehicle in case of quick stop.
Stuff more blankets to restrict movement during transport.
Your brother should make sure he's in control of the speakers the entire time. Others are not invested enough to know what is fragile and what isn't.