You can "unlink" the child shape size from a parent group, by making some adjustments in the shape sheet. In the example below, you can see that the size of shape "Sheet.3", is a formula based on the size of the group named "Sheet.1". By replacing this with a fixed number, you can unlink the size from the parent shape. Typically you will want to leave the PinX and PinY still related to the parent shape, to move it along with the group. If you have a group with multiple shapes, there is as far as I know no way to do this for several shapes at the same time and you will need to adjust each individual shape sheet for each of the child shapes.