My Dad has gone down hill rapidly. What can I do?

My brother moved in with my parents in the last month after being out of state for 30 + yrs. Be didn't move on as a caregiver, but to save money. Him and his dog have overrun everything and now my Dad's episodes of confusion are daily. They used to only occur when he didn't use his cpap, but now it is everyday no matter what. My Dad now thinks this isn't his house that he has lived in for 55 yrs and he thinks he is trespassing. He has been getting more agitated and I think it is because my brother has upset the norm. My Mom & brother don't believe this change could do it and think my Dad is crazy. What do I do? My brother will soon be moving his girlfriend in & I'm afraid it will kill my Dad. I want to do what is best for my Dad, but my brother is selfish & my Mom feels sorry for him because he has money issues & was recently dagnosed with type 2 diabetes. No one seems to want to help my Dad but me & I'm not sure what to do.