Kidney infection? I hope they are ok!
I put the game cam in the bathroom to find out that it was my female cat. She's still using the sink, but right now that's actually good so I can monitor her blood loss. Never thought I'd be encouraging the cat to pee in the sink.
The blood seems to be reducing in quantity. The vet treated them both just to be safe (again last night we could only guess which one it was).