What can I do to ensure my dad is cared for the way he should be?

A few years ago my mother passed away. My dad needed alot of care and surgeries to be strong enough to live on his own. I quit my 10 year job to care for him and see him through every moment of our 32 trips to ER and 5 facilities. I left no stone unturned researching and double checking meds and bills and getting him reimbursed and countless hours on the telephone with insurances and learning what the policy under the policy of the policies were etc. I worked countless hours for him and did a great job no matter if I had time to grieve or was grumpy etc which is all someone can say in regard to the cons of my behavior of what I went through. Only to be shockingly accused of in the end-took two years for someone to simply tell me that I was being accused of waiving my closed fist in the air and looking at my Dad and that it was in front of neighbors so Im assuming outside in the front or in the garage when his buddies would come see him once he was home. It took two years of being left in the dark left to question on a daily basis what it was I had done to constitute just being completely dropped and not contacted etc by him. Granted during the time he was referring to he was on Norco, and morphine at times and finally put on methadone to come off of as well as deluded a whole bunch of meds that I'm more than sure helped him think this really had occurred which now we have been back to speaking for a few years and he finally remembered the other day and made a comment that he realized it may not have been real. Before all this my sister asked if it may be a good idea to become his POA and care person and maybe we build out Dads house and we can all move in and help with dad But fast forward she went ahead and had a small unit built with my dad's money and a small percent of her and her husbands money that went to have a bathroom added onto my parents bedroom in the main house. She then tells me my father lives in the house in the back, which didn't sit right with me. You don't take an elderly parent out of the home they shared with their spouse and stick them in the backyard where they no longer get to see the activities of their street. That'sin a his main activity and window to the outside world whichhad already become smaller because his best block buddy and my mom (his highschool sweetheart of 50 years of marriage) passed unexpectedly and last month. He also lost his only sister. Anyhow, I get a call from her and her husband telling me that my dad was in the hospital and that a social worker was calling questioning them and they hung up on her instead of answering all her questions which is what a normal person would do. So, they ask me for my assistance and have me go check things out at the emergency room for my Dad. I hadn't seen him in about two months because of the family dynamics that seem to be occurring and not being able to do anything about it. Upon my arrival at the emergency room I ended up walking right past him. His hair is now long, uncut and stringy. He has a grizzly adams beard that had me questioning how he'd even eat food with it. It threw me off because his appearance was not his normal. I felt he has been neglected in terms of hygiene. My sister does cook and bring him his meals, but the hygiene alarmed me. The social worker walked up and spoke with her and it turns out my brother in law kept interrupting the conversation with my sister and just wouldn't stop. At any rate I haven't heard from her again. At one point my Dad was voicing how he didnt want to go back there to live with them because all he hears is them arguing and my nephew who is an adult with asberger's telling them to shut up and stop it. It's high stress around his son in law who treats everything as if it's an annoyance. My sister has PTSD and anxeity. She drinks and I'm not down on her, just saying everyone has something including myself but it interfers. Anyone have this kind of situation?