In this case you should have an "Equipment Prototype" as parent for all your clamps.
From your structure in Object Tree put all clamps under "FIXTURE" into an "EP".
You can open the Kinematics Editor for the EP as well.
On EP selected you can also open the Pose Editor and you can select the poses for each clamp.
So you can simply build the different steps of you fixture.
You need a dummy kinematics inside your EP.
Custom create two links and a joint between.
As long as this is not available the EP is not interpreted as device.