Very subtle elder abuse, please help.

My 89-year-old dad is so influenced by his care giver of 9 years that he turned against his own family. His mind is pretty sharp. She has stolen money and he protected her. He gave her half the property and is so attached to her. An APS investigation would kill him -as he gets very scared when the matters related to the issues at hand are brought up. I dont know what to do... There are more details. Please help.