Attach transfrom controls to center of Group?

I am creating One Group and adding Plane and sphere inside that group. Then I attached Trans Form Controls to that group. Trans Form control are getting attached to group and if I move the group with Trans From control plane and sphere both are Moving Which is what I wanted.

But Position of transform control is not at the center of Group.

I want exactly like this which I created in ThreeJS Editor

What should I do so Transform controls will be at center of Group. I don’t want to change position of my plane or sphere this are important. One Approached that I tried is

transformControls.position.set(plane.position.x,plane.position.y,plane.position.z)

This change the Transfrom control position to center of Group but does not change Pivot point of transform control which is at center of scene so all my rotations of group are around that point.