You can select multiple openings by dragging a marquee across them or using the shortcut Cmd + ClickCtrl + Click to add or remove items from the current selection.  A group of selected openings can be dragged or re-sized the same way as a single opening.

Holding the Shift key down while dragging one or more openings will cause them to only move horizontally or vertically from their current position (whichever is closest to the mouse pointer).  Holding the Shift key down while dragging a re-size handle, will force the opening to maintain the current aspect ratio (width-height ratio).

By default, when you re-size a selection of multiple openings, the Editor will attempt to keep the spacing between the items the same while only scaling the size of the selected openings.  This works best if all the selected items are in the same row or column or if you have multiple rows/columns with the same number of items in each row/column.  If you wish to re-size both the opening and the spacing proportionally, then hold the OptionAlt key down while dragging on a corner.  Holding down the Shift key while dragging will keep the same aspect ratio.