I need advice please

My fiancé parents are letting us rent they're home because they bought a new home. Anyway my sister and her family became homeless and I'm letting them stay with us for a couple weeks. Well his parents called CPS on them because they don't want them staying with us and told CPS that my sister is pregnant and on drugs (WHICH IS NOT TRUE) and it's creating a whole ton of problems with me and my fiancé our families and everything. We are getting married in one month and I don't know how to handle this anymore. Any advice or anything could help me right now.