I've looked through several operators manuals and service manuals and nowhere in them does it refer to multiple persons in the operators compartment. It only refers to the operator in a singular term. It does not specifically say that multiple people can not be in the platform area while operating the orderpicker , it only refers to the operator in singular context.
Which is why i previously said, they only design orderpickers for one operator only, not even a trainer would be an exception imo if the compartment was not designed for more than one person.

Now if the truck was designed for a 2 man operation and accomodated enough room for both of them to fit comfortably in the station they were intended to be at then sure... ONLY then would there be more than one operator allowed.