How to prevent Image sprite overlapping

Suppose I have 2 image spirits which change their position continuously. one on them is controlled by user using joystick. When they collide I have made few blocks to change their direction replicating elastic collision formula. However as user is controlling one of the image sprite the direction do not change , and image spirit overlaps.
How to make a restriction that they always bounce each other and never overlap.

use the CollidedWith method

or are you talking about the so called Sprite Cannibalism?

When more than one ImageSprite can be dragged on a Canvas, unless precautions are taken beforehand they may get ‘stuck’ together. This is referred to as ImageSprite cannibalism.

see also