Updated: Jan 9, 2019
Two queens + one hive = lots of honey!
The system I’m describing is a horizontal system in that two colonies are placed side by side so they can share a common set of supers. The colonies stay physically separate although I prefer to join the bottom boards with screws. This ensures both sets of brood chambers are at identical heights even if the assembly is placed on a slightly uneven surface.
The Two-queen Horizontal System
by Bill Hesbach