Im pretty confident all hydralic steering sytems can handle twins! but depends on weighting!
Ive been involved with a twin 40hp rig which was suposed to be a single engine only kit. The system was rated at 200hp+ so we added a simple, adjustable tie bar and works perfectly!
I'm also aware that some of the larger more expensive systems are capable of 'true' twin systems using the same helm pump, an extra steering cyclinder and 2 special 2-way boxes! This was heavy though (twin evi's 225 but non counter rotating originally) and soon converted to power assisted