5 week old rats with mites/lice??? HELP! (first time rat owner)?

I only really know the answer to the wet spots... Either they're sitting under the water bottle, or they have 'wet tail' disease. Seeing as you have only recently bought them, you really should take them back... they are not healthy. But don't worry about the sneezing, my hamster used to do it all the time, but its her third week in my cage and she's stopped. However i didnt use sawdust in her bedroom when she was sneezing but I don't know if that was what helped..