Okay, the 10A, 12A, 13B, 13B-T, 13B-REW (TT), and the 13B-MSP (Renesis) are all 2 rotor engines. The largest rotary produced was on the limited edition 90's Cosmo that came as a 20B-REW (2 litre 3 rotor TT) design.
The custom fab'ed 26B and 26B TT designs are basically two 13B-REW's bolted together with longer custom engine bolts and a custom eccentric shaft. The result is similar to having two twin turbo RX-7 engines under the hood, but the conversion is costly and complicated to tune. This setup has been a known favorite among drag racers and easily puts the car close to or over the 1000 hp mark depending on tuning.
Watch this video. Imagine the exact same thing, but with two more rotors and a turbo system. This is the assembly of a renesis. Rotaries are put together alot like sandwiches, and the eccentric shaft runs through the middle and works the same way a normal crankshaft would.
http://www.step-hen.com/rx8/files/renesis1.wmv
This is the actual assembly line in Hiroshima. Yes, the engine is entirely built by hand in the Mazda plant.