How can I make characters push each other using physics?

I would like to develop a setting in which the characters naturally push each other due to the difference in their masses as they crash upon one another.

So I tried to do so by turning on the simulator physics option in the Mesh only to find that the character freezes in such a setting.

I think it did not work because the AI Controller itself is non physics while I tred to move my characters using the Behavior Tree of the AI Controller.

I have to use the PhysX of the Unreal as well as the Behavior tree of the AI Controller to move my characters.

If you are aware of any tutorial or URL that teaches a method to deal with AI using physics and BT, please let me know.

Thank you.