The cats have a date with the vet on the 14th November.
On Facebook I'm part of a cat group and I shared a picture of Rowan and his tail. When he's happy (and expecting treats or food), his tail runs parallel with his back. It also quivers if he's excited. Anyway, most people on Facebook said he has a double-jointed tail. Someone else said he's an American Ringtail. Ringtail cats usually have their tails curl right over, almost into a circle. They were bred from a stray cat who had the trait.
I look forward to asking the vet (his name is Ewan, we always see him) about it.