you can change the the pivot point of an object by hitting the insert key (0 on the righthand numberpad) and moving the pivot to where you want it then hit insert again the complete the move.
If you have more than one object you can group them using control + g and then hit insert and move the group pivot point.
When you want to animate the group select one of the objects and hit the up arrow key until you reach the group and then you can rotate it from your chosen pivot point.