Wiring the hands
Point helper for the wrist. Select the IK handle and link to the point helper. Moving the point helper will move the arm.
Remove the rotation of the hand – hierarchy panel > link info > select palm and remove all the rotate checks.
Wire parameters
You want to control the rotation of all the joints. We need to create a controller that will control all the fingers. Create a point helper. Wire the rotation of the joint to the rotation of the object.
Select the joint, right click > wire parameters. Left click option > wire the transform > rotation > Y rotation. Click on the helper transform > rotation > y rotation.
Then get dialogue box. Controlling the middle finger from the point object > chose direction to the joint that you are wiring. Click Connect.
Now if you rotate the helper it will rotate the joint. You need to repeat this for every bone in every finger.