trouble with in laws?

Okay so we are currently staying with my in laws and I always make sure to do work around the house and make sure everyone nice and clean. However, my fiancée has a 16 year old brother who does not do anything around the house because of good grades. His mother still makes his bed and cleans his room and always makes her do things fast to cook him dinner, clean his room and makes her feel bad for buying herself things.  Since she's out of town, I'm doing his bed but he takes advantage and he told his mom that I'm being rude and don't want to clean his room. I am mom also, and I have my child to care for and it's doesn't bug me to cook or clean. What bugs me is the entitlement and how easily he thinks I have to do things for him. He basically snaps his fingers at me. I don't mind making food for him but he can't even put himself cereal without him getting angry at me. What do I do?! Before I go haywire?!!  I have to clean his room and make his bed and even pick up his clothes before his girlfriend comes over. His excuse" I have good grades so that's the deal with my parents"