What is the maximum number of specials that can be alive at a time?

In Vermintide 2, what is the maximum number of specials that can be alive at a time? (Where beyond that maximum, the AI director will no longer spawn specials.) Also, is there a maximum of the same special unit type allowed at a time, and a maximum of disablers allowed at a time?

Please specify differences if there are any, between the difficulties, especially Legend and Cataclysm, between the game modes (Campaign and Chaos Wastes), and if the "Seek and Destroy" deed modifier is applied (described as: "specials spawn with much higher frequency and in larger numbers").