I have brought (and will continue to bring) all sorts of foods into the UK, including Twinkies and Zingers. I've never had a problem, and I have never had to claim anything. I think that as long as you are bringing in commercial foods, in small amounts, for personal use, you will be just fine. That is, to clarify, not including meat, eggs, "fresh" foods, if you will. I've never brought in produce...just pre-packaged, preservative laden junk--you know, REAL food ;-)
Enjoy your visit with the family!!