Step 1: Have your sibling stand against a wall. There can't be anything on the wall like lightswitches. It can only include your sibling.
Step 2: Hold up your magnifying glass so that half of it is in the shot. Make sure that parts of your sibling are visible around the sides of the magnifying glass. The curve in the glass will show a different part of the wall instead of your sibling, thus making it appear that your sibling is invisible when looked at with a piece of glass. Now go show your friends that you live in ghost family. It might get some interesting reactions. :)