My sister's have taken "control" over my dad. They do not allow any communication between my parents. Does anybody have any suggestions?

My parents have been married for 66 years, had 4 children, 10 grandchildren and 15 great grands. My sisters have put a wedge between the 2 of them, the sisters do not answer phone calls, text messages or answer the door when my mom tries to contact my dad. Dad has declined in health over the past 2 years, and his dementia has worsened since March 2019. The sisters manipulate my dad into believing that I am taking advantage of him and my mom. Mom does have a diagnosis of dementia, however she is able to make her own decisions, unlike my dad, but he has expressed he wants to come home and be with my mom his wife. They refuse to let this happen. They have only allowed them to see each other for 1 hour total since June 1st!! Not only have they cut off ALL communication between the 2 of them but also none of them come to see my mom! My daughter and I are the only 2 that are here for my mom, the sisters have even gone as far as to tell APS, my grandchildren are not allowed over here! In my opinion they have tried to completely isolate my mom from the outside world! Telling untrue stories to my mom's own sisters, lies about me!