You’d really be better off changing the skeleton.
On this one, you don’t have to change the weightpaint at all.
You just need to make the wrist part parent to the lower arm, disconnect from the wrist, and connect up the lower arm to the wrist.
It would match the unreal skeleton somewhat.
You just don’t/can’t change the position of the wrist twist bone. Or maybe you even could, it depends on how you do it / the existing weight paint.
Having a bone chain is bad for a lot of reasons. Unless you are planning on making a marshmallow man when you trigger ragdolling.