My father in law is being neglected by his daughter who lives with him and she won’t move out

Do we have any legal recourse that doesn’t end in him being removed from the home instead of her?

Location: California

Obligatory “typing on mobile so please excuse any formatting errors” disclaimer

This may get pretty long but some background, my father in law owns two houses next door to each other. My husband and I moved into one and shortly thereafter my sister in law moved into the other with her then fiancé. My sister in law is an alcoholic and has been for the entire 26 years I’ve known her. Her fiancé wasn’t a bad guy at first but eventually he got addicted to some pretty hard drugs. My father and mother in law asked us to help evict them from the house. We hired a lawyer and sister in law waited until the last day when the sheriff had to kick her out.
Unfortunately my mother in law passed away a little over 2 years ago, my father in law was crushed. It took a lot of work and coordinating a lot of people but we were able to get the house next door in livable condition (sister in law trashed it). My father in law got sick and was hospitalized so we rushed to get furniture so that when he was released he could live next door. We were juggling taking care of him as well as our own little family, we have a young daughter. I’m not sure if my father in law felt guilty for having us take care of him or what but a couple of weeks later he brought sister in law to live with him to help him out and to help drive him around, the same lady that showed up wasted at her mom’s funeral just a few months before.
We obviously wanted nothing to do with sister in law who at that point was nearly 60 years old with no job and got by by living off of other family members that took her in. She literally had nothing to her name. We stopped visiting and helping FIL when he basically told us that he didn’t want our food we brought him if we were unwilling to also feed SIL. We didn’t go next door in an effort to shield our daughter from SIL’s antics.
That brings us to last week. On 4th of July we saw FIL through the window with no shirt on and we were floored. He was so emaciated he looked like a prisoner in a concentration camp. My daughter immediately wanted to feed him so we took hot dogs over that night. Guys! The whole house reeked of urine. We gave him the hot dogs and were completely stressed all night. The next day we brought him eggs for breakfast and we learned that he only took 2 bites of his hot dogs and didn’t eat his eggs. We heard SIL talking on the phone with her friend saying that he hadn’t really been eating or drinking for a week now. We called 911 and had him taken to the hospital. When paramedics got there SIL claimed that she must’ve called 911 at the same time we did but she never called. We found out that she had been telling people for 2 weeks that FIL was going to die in a few days but never called for help.
Now we are trying to take care of him but it’s hard being next door. I am willing to move in with him to help but SIL won’t leave voluntarily. We have documentation of a lot of her neglect, pictures and videos as well as the doctors reports from the hospital. He was in terrible shape, had we not acted when we did I have no doubt he would probably be gone by now. I’ve explained a lot of the situation to the home health nurses and I’ve asked if a social worker would be coming over based on the shape that he was in and she said yes but we haven’t seen one yet. I’m only afraid that if we report her as being a danger to him that they will take him away rather than her. Anything I can do? If you have any questions feel free to ask. Thanks!