SIL and Husband arguing

So my brother and my sister in law are currently living with me and my husband as we opened our doors for them when they were in a tough spot. They have been living with us since July. The plan was for them to save enough money and to move out. They do not contribute to any of the Bill's with the exception of half of the electric ($100.00 monthly) yesterday my husband bought and put up fall decorations in our guest bathroom which is the bathroom that my brother and Sil are currently using. He was very excited about putting his decorations up as he loves to decorate our house. My Sil and brother got home and she started to complain about the bathroom. She was upset that we moved all her makeup that was throw in the bathroom and we set it under the sink. We cleaned the bathroom as it was nasty. Anyways she came home and threw the decorations out of the bathroom and into the hallway. My husband was then livid. He got upset, because he finds it disrespectful to throw our stuff out that WE paid for. She stated she was trying to clean the bathroom and our stuff was in the way.. she also stated that she should have a say in the decorations since she lives there too... my husband seems upset with this comment, because she doesnt pay anything and he likes to make the house to his liking. Now this has become a issue and a big argument. I'm just not sure what to do, what to say or anything. I'm not sure if I'm looking for advice here or just a place to rant. I just hate the arguing over little things :( but I understand what my husband is saying too.