This might be a stretch, but the two birds in the middle of the circle - the one on the left looks different to the other. It looks smaller with a finer beak. There was another one in another photo again on the left preening whilst a Caspian Tern on the right is preening and it looks different? They were a long way off pics blurry.
From what I can see they all appear to be Caspians with their large size and chunky red bills (Whiskered are significantly smaller) with a few Silver Gulls in there too.