How to create physical behavior for a robot gripper/hand?

I am working on a simulation project. I have a three finger robotic gripper. All the fingers joint are rotating around an axis.
In simulation, I need to grasp one bottle and release it in different orientation on the table. That’s why I need the physic behavior be enabled on all joint and rotate them by applying torque or force.

The problem is, I don’t know how properly setup the fingers and wrist together, with enabled physic and torque control.
Currently I put them in parent-child hierarchy in a blueprint, but when I enable the physic for fingers they all fall down because of gravity. I applied the bone chain in Maya and import the model into UE4, but I faced the problem of proper collision shape (they are very basic).

I appreciate it, if anybody could share his idea to resolve this problem.

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I came across your question and I would like to ask if you got it to work and grasp objects by physics?