How to convince a caretaker they are being unkind to spouse with dementia and also allowing adult son to push spouse around?

A friend recently visited her parents. Her 92 year old dad has beginning dementia but is unable to drive now and is pretty forgetful. She observed her mother, his caregiver, being continuously critical and mean to her dad. Her dad seemed to be in pain when he stood up from a sitting position. She asked what was wrong. Her dad replied that his adult son, who has always lived at home and is in his 50's, kicked him in the rear end. When she confronted her mom, the mom made excuses for the son and said he didn't kick him that hard. She, and I, are very worried about her dads well being. The mom who has some medical problems, relies heavily on the son for driving, emotional support, etc. my friends brother has some kind of personality disorder and is over 300 lbs. My friend wanted to take her dad for an exam to see how hurt he was but her mom objected. She didn't do it and now greatly regrets it. The mother absolutely will not kick the brother out and between the two of them they seem to be blaming the dad for his dementia. They complain he can no longer do home repairs and say he's pretending that he had forgotten how to get his own lunch. My friend wants to have her dad attend a daily adult day care, but the mom refuses bc it costs money. My friend wanted to take her dad home with her for a week but the mom refused. My friend would even have her dad live with her but again, the mom refuses to acknowledge there is a problem. Plus, the dad himself doesn't want to leave his home and thinks his wife is going to take care of him. It is heartbreaking. My friend does not know how to proceed. Should she report her brother? If he is removed from the home he had no where to go snd her mom would never speak yo her again. She also worries the brother may go back and take it out on the father. She believes her brother is dangerous. The mom says 'she can keep him under control' but I think this situation is a ticking time bomb. Please advise. My friend and her family live in California about 400 miles from each other. She has 2 sisters in other states who have also witnessed the meanest towards her dad from the mom, but no one wants to pull rank in the mom who pretty much rules the roost. If dad is removed from home thru worry he will decline more rapidly and pine away for his wife.