Mil help

Alright so my husband and I have been married two years almost. My mil lives with us. When my husband got our current home he wasnt thinking and basically they decided one end would be our end and one would be hers. Well she seems to also think the kitchen and living room is too and she can decorate it how ever. She also has 2 foster kids that are their family members kids but she has custody through the court. Anyways she has health issues and cant live on her own due to not enough income. She does pay rent but wouldn't be able to find her own place for what she pays. How would you handle it with her and any ideas how to solve the issues? She throws a fit like a toddler jo joke. Screaming, crying, cussing, stomping ect.