Seasonal Pitch sharing

I'm new to caravanning having bought our first tourer last year. One of the main reasons that we took the plunge was that my elderly parents had just sold theirs as, at 80, towing and pitching up was getting a bit too much for my dad. They have enjoyed camping and caravanning for many years and with various mobility and disability issues now can't really have a different kind of holiday over having their own van. So it seemed a good solution for us to own it, take it to site, pitch up and then mum and dad take over. They have retained their club membership and so I thought we could book a seasonal pitch on their favourite site, my wife and I would have a week, then my parents would take over for a couple of weeks and we would have another week at the end. However according to club rules this would be sub letting and not allowed. Am I wrong to think the rules in this respect are a little draconian. Having rung the club about the rules they wouldn't budge saying that we would have to pay for the time we were there and my parents (there for longer) would have to book the seasonal pitch.