Purchase or borrow a couple of unopened bottles of beer, and also get your hands on an empty bottle. Carefully rinse out the empty bottle, and then fill it with sparkling apple juice. When your in-laws walk in, have the open bottle of juice in your hand, and then take a long pull from the bottle. With your other hand, extend the unopened bottle of beer as an offering. When they inevitably say something, tell them that you only drink on game days, and if they want to visit during a game, then they need to deal with it.