What do I do when the elderly family member is the abuser?

I'm a part-time caregiver/mediator for a friend. I regularly have to de-escalate situations between the grandmother and every other member of the family. She is extremely manipulative. Her behavior would fall into the "well intentioned but unhelpful" type of quirks,except that when she thinks she isn't being observed, she becomes much more capable and destructive in ways that target people personally. - She is partially deaf, meaning everyone needs to repeat themselves and she yells at everyone... ...but there is no record of it medically, and she regularly eavesdrops by listening against doors and windows (we can hear her fumble around when we approach doors and when caught she pretends to be "stretching her legs") - She likes to clean the house... ...but she does it by breaking into locked or otherwise private rooms (she has damaged locks, removed safety tape over electrical systems, and even entirely removed a doorknob), then usually breaking objects, taking favored items to hide until later (we've observed her planting then "finding" them around the house later as a reason to yell at someone for being "careless"), or outright disassembling things that prevent entry - She does the laundry sometimes... ...and items that people express favor towards (favorite shirt, comfortable undergarments, etc) end up in the trash. She pretends she doesn't know where they went. - She cares deeply about the pets... ...except she has gotten multiple pets killed with "home remedies" or "cleaning accidents". Remember how she breaks into rooms and messes around? One room in the house has a single switch that toggles the power to the whole room. That switch has tape thoroughly covering it (literally impossible to flip) and a sign directly over it that explains that the animals will die if the switch is turned off (temperature controls/incubation/etc). This tape was of course removed, the sign nowhere to be found, and the room was cold when the family member who owned those pets got home. RIP chicks, almost RIP snake. She also permanently blinded her grandaughter's emotional support dog with a homemade abrasive "eye wash", necessitating the dog being put down. Her defense is usually saying she didn't do anything, then saying it wasn't her fault, then saying she doesn't care if something/one was damaged because nobody is ever thankful for her help. I said before that she targets people personally, here's what I mean: - She knows that the autistic grandson won't confront her, so she berates him for things he can't defend himself over and blames him for everything she can, but only directly at him and she thinks nobody else is listening. - She knows that the granddaughter with the service/emotional support animal requires relative peace without interruption to work (artist) and a safe place to decompress with her dog, so she repeatedly bothers her (and ONLY her) with inane but harmless questions (did you eat? did you see the new bottle opener I got?, Do you know where the remote is?) which she of course "can't hear" the answers to, until the granddaughter becomes "disrespectful" by raising her voice, which leads to grandma standing near the closest open window yelling about how terrible of a granddaughter she is. This almost always ends with the granddaughter losing her composure entirely with a full blown anxiety attack, complete with screamed responses. - She knows that the mother and father are relatively straightforward, so she goads them by saying things like "I wish you had died instead of my other son" until they slam a door, then starts reciting every failure she can think of as loud as she can until they lose it and leave the house. - She knows her husband won't speak up unless it's an emergency, since his indifference towards her antics was legendary even BEFORE he had a stroke and his attention span took a hit. They are both very clear that there is no love between them, they just don't believe in divorce or separation. - The only member of the household she doesn't go after is the minor, who from the moment he joined the household (as a teen) has ignored her, worn earbuds, and never let her learn anything about him. In a recent case, she cornered Mom, berated her, then struck her, leaving cuts. Grandpa stepped in, managed to separate them, but also somehow broke his arm across grandma's face causing a black eye. The police have informed us that no matter what she does, the elderly are a protected class and any injury is an aggression by the younger party, because they are expected to control themselves and defend without letting her hurt them. Multiple people in the household have developed suicidal ideation and have had to have been removed from the home for up to a year, only to relapse within a few hours of re exposure to her behavior.