A relative has decided that his listening room is too small for his RM40s and he has asked me to take them, give them a listen ... and to enjoy them.
Hi SpeakerDoc and welcome to the VMPS Circle.
LUCKY YOU!!

Sounds like you hit the Audiophile Lottery

I am wondering exactly what these are, the boxes say:
Soundcoat
Megawoofer
Auricaps
I assume that these are options.
Yes those are options. Megawoofers and Soundcoat were actually standard on the RM40 model.
How is the Megawoofer(s) different?
In general the MegaWoofer is simply a heavier duty woofer. Cone materials are lighter and stronger, Magnets are bigger and stronger, and Baskets/frames are built for higher performance.
I read that these are 4 way, and there are 2 10" woofers and a passive.
They are actually 3-way with XO points at 280Hz and 6.9kHz.
Do the 2 - 10" both handle the lowest bass, they look to be the same driver?
The lowest bass is handled by the bottom 10" and the Passive radiator.
The upper 10" is called the "MidBass" woofer and blends to cover the higher bass frequencies. In the newer models, they are exactly the same in construction but Brian has "magnetized" them at different strengths to cause them to be more selective in their responses to the frequencies he wants them to cover.
They have the FST tweeter and have been dehorned.
I have both standard grilles and the type with the CD slot. I believe that the crossover mod was done for the slotted grille.
That would seem likely if they were dehorned.
How do I get to the crossover to confirm this?
You might e-mail Brian with the name of the original owner.