How do you get the APS case worker to actually investigate what's really going on and not just take caregivers word for it?

My father in law is a Korean War Vet and needs care at home. My mother in law says that she is giving him great care but this is not true. My wife (his daughter) was asked, in January to come help take care of him. She willingly went to San Antonio from Dallas and stayed for a month. She was made to do all the care for him during her stay. She also stayed with him the 2 times he had to go to the hospital because the mother in law would not. My wife actually had to talk to all of the doctors and nurses and set up all the therapists with the VA as well because the mother in law refused to. During her stay, following all the orders for feeding, medications, and therapies my father in laws health improved greatly. After this happened, the mother in law (who by the way is 2nd wife) had a meltdown and kicked my wife out of her house and started isolating him from everyone. I heard this meltdown on the phone because my wife called me while she was packing her clothes to leave and I could hear the mother in law yelling at her and everyone else in the house including my father in law. When she returned to Dallas, she would call to speak to Dad every day and you could hear the mother in law in the background basically telling him what to say. He has been diagnosed with dementia, Alzheimers, and Parkinsons so he gets confused and upset so its no problem for her to make him say what she wants him to say. My wife returned to San Antonio about 10 days later and stayed with her step sister (mother in laws own daughter) for 2 weeks. During this 2 week stay she was only allowed 1.5 hrs total of visits with her dad. When my wife saw him she took a picture of him and it is obvious that his health had declined dramatically. She was told that the doctor had ordered no visits more than 45 minutes at a time. My wife contacted the doctor and he has no record of any such thing. In fact he had not even been to see him since my wife left. At this time, my wife called the APS and the case worker went to the house and says he questioned the mother in law and her 2 friends. There is a long list of evidence and witnesses to dispute what the mother in law says and he does not even want to hear it, he says that it is all hearsay. She has isolated him from his family, she won't let him speak to visitors without being in the room coaching him on what to say, she has even said, in front of witnesses that she just wants to drop him off at his granddaughters house because he's not worth the money she getting from the VA and his SSI, she won't bathe him regularly and keep his bed sheets dry and clean, she leaves him while she goes out until 1 am, she constantly verbally harasses him, she has history of abuse to others (her daughter), she withholds affections from him unless she thinks some one is watching, does not allow regular visits (even lied and said that was doctors orders), lies about things my wife and others has said, does not follow instructions on feeding and therapies (even lied and said that since she put him on hospice he cannot get therapies) and takes his money from his account and moves it into one of her 6 accounts. She is being paid as his caretaker from the VA but leaves him alone for long periods of time or has one of her 2 friends stay there while she is gone. Neither one of them does a thing for him, in fact if something happened, like him falling, neither one could get him up. She does not even give him his medication regularly, only if someone is coming to see him and tells everyone that he does not want to take them, the doctor told my wife while she was there to crush the pills and put them in pudding but the mother in law thinks that's just too much trouble. The list goes on and on. My point is this, the case worker is not investigating to see if what the mother in law says is true or not he just takes her word for everything. My wife has given him phone numbers of witnesses and has exposed her in lies about everything but he doesn't want to hear about it. He says that everything is fine and there is no abuse because the house is clean and the mother in law says everything is fine. What can we do, because guardianship is so darn expensive. We just want this man in a safe place where he can get the care he needs so that he can enjoy the rest of his life and not just be a bed ridden old man waiting to die. It has been proven that with proper care his health improves but the mother in law either does not want to or it's too much trouble for her too. APS has done basically nothing to help what can we do?