I think Whale is right, it sounds like they have gone a bit overboard on the concept of “commercial”. Even if you are holiday letting, it is still residential, same as if it was a normal tenancy arrangement.
Setting that aside, I don’t think the owners corporation can decide that two lots are liable for the cost of the inspection unless they pass a by-law, and in that case the owners responsible for the costs would have to agree to the by-law. I could be wrong, but l believe they are on shaky ground. If they billed you, I would just refuse to pay it.