Kim he is gorgeous!! I'm sorry but I did have to giggle at the second picture. Looks like you caught him in the act. I'm sure you are very frustrated. I have no idea if neutering will help the spraying issue but hopefully it will.

As for the URI, it doesn't automatically mean he isn't up on his vaccinations. Ripley has always had his annual vaccinations yet he still caught Jazz's URI when we first adopted her. Of course from what you've told us about the guy who dropped them off it does sound like he probably didn't take the best care of them.

Good luck.