Mawgan Porth is a dog friendly village, with all kinds of accommodation. Some of the hotels have no limit on the number of dogs, but I don't know about the self catering situation.
We found out about after stopping to chat with a couple holidaying with their two cavaliers. they said their hotel was lovely and that there were 9 dogs staying there, including a Great Dane. The name of the hotel contained the word 'White' (Gables?) and is the one that advertises in doggie magazines.
After Googling the bvillage, though, lots of 'no dogs' places come up, so perhaps things have changed.
I do know that places willing to take more than two dogs are generally difficult to find, as was found by my dog trainer who had four; three shelties and a border collie.
Try joining Dogpages and ask there. People often, do and get good responses.
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