the answer to both questions is the same. You have to use the 'Scale' command. Whether it is a single object or a group of objects. The only caveat is that if you want them to change not on their single axis but on the group axis, you must ensure that the "Centre" option is selected instead of "Pivot". This also applies to rotation.
Once you have selected the object, or group of objects, hold down the "Shift" key and left-click on the square that appears at the centre of the "Scale" pointer, moving the mouse up or down will increase or decrease the object or group of objects proportionally on all axes.