The wheels are 12". When loading the trailer, the larger wheels do make the angle of the hulls a lot steeper (along with the mast angled back further) before the center of gravity of the boat is past the back rollers. At that steep of an angle it also puts a lot of stress on the rudders against the sand.
I don't put the trailer in the salt water. Unloading/loading, I put the trailer wheels just short of the water's edge. Unloading is pretty easy.
I used to stand on the trailer frame and pull the boat up onto the trailer using the dolphin striker rod. Now I manually pull the bows up onto the trailer's rear rollers and then use the trailer's 25' x 2" winch strap/hook wrapped around the front crossbeam (next to the mast step) to winch the boat up onto the trailer (so much easier on the back and you can stop winching when the transoms are just out of the water to open the drain plugs).
I am 68 today and usually sail solo, guess I should have asked for beach wheels for my BD.
The lights are sealed LED submersibles.
The guy in this video has a really big trailer:
https://www.youtube.com/watch?v=mEKE4owuah4