I didn't notice when I first posted that you were from the UK. I can definitely see why you wouldn't want to bother with GMRS FCC license. In the past, we have used FRS radios that were the Cobra brand and they worked fine. We were using them in off season,however, so our experience may have been better than others who used theirs during times when the crowds are heavier. I highly recommend that whichever brand radio you buy, probably the single most important feature is that they have the sub-codes. This will give you a much greater chance of finding a channel that isn't being used as much. You will likely hear "chatter" from other users, but if you don't plan on splitting up a lot and you only turn them on when your party is not all together, then it's usually not that bad, IMO.
HTH and have a magical day!