Maybe reference England, rather than the UK, for the Calais answer? Otherwise several French cities are closer to the Channel Islands of Jersey and Guernsey.
Like the Isle of Man, they are Crown Dependencies. Self-governing, but possessions of the crown. So Kalleanon is correct, they are not part of the UK. https://en.wikipedia.org/wiki/Crown_Dependencies
Last answer is incorrect - Anglesey is larger at 276 sq. miles cf. 221 for Ellan Vannin (in Manx). You could also either ask for, or at least, accept the larger one's Welsh name (Ynys Mon) as an alternative.
Disappointed to only get 3 points (17-of-20), but pleased to have gotten the least-guessed answer, Pitcairn Island. (that always seems to be a very nice consolation prize when you don't do particularly well)
Ness : A river that flows from Loch Ness
Inverness : City on the mouth of the river Ness, near the Loch Ness Monster.