Yes, he absolutely does.
If you thought Kenny's older brother is completely unimportant to the story, just check out his sister Karen. You might be wondering why this picture of her is so blurry. It's because she's never spoken and has only appeared a few times in the background; this is the best picture we can get of her.
Don't completely despair; you may have noticed Kenny has been focused on a lot more in recent seasons (Major Boobage, The Ring, The Coon Saga, Poor and Stupid), so maybe they'll finally get to showing his siblings.