Multipoint then move area


I am trying to set up a digital planing software for orthognathic surgery. I found posts on how to do cephalometry with multipoint selection (which works fine).

My problem is: after marking several points I would like to cut out a part of the picture (including the contained points), move and rotate it for some mm, then recalculate the angles and distances between the point in my segment and the rest of the picture.

But if i try to select an area, the multipoint selection disapears.

I am grateful for any suggestion.