Hand IK Mesh Deformation

I´m not experienced at all on animation, so I apologize if this is a simple thing that I haven´t been able to figure out.

I´m wondering how games like The Walking Dead: Saints & Sinners go about having deformation in the arms to match the position and rotation of the hands.

I followed this tutorial, but in this case the hand just rotates in place instead of making the whole arm deform with the rotation. I’m guessing that maybe this has something to do with the way a skeleton is exported and the default UE4 Mannequin does not support this.

I don’t know a lot about rigging either, but I use Mr Mannequin Tools for everything. Inside Blender, rotating the hand does actually rotate the forearm as well, but I don’t know how to replicate this in Unreal, could somebody help me with this? Has somebody done something similar?