How to handle safety issues and family disagreements?

My 84 year old dad has dementia, paranoid personality disorder, and Parkinson's disease. He has recently started telling my 82 year old mother to leave the master bedroom, that he doesn't want her in the bedroom and he doesn't want it cleaned. He accuses her of stealing things from the room when he's not in it. He has decided he wants a keyed door lock installed on his door so that my mother cannot enter, My mother has started using a room across the hall from the master bedroom and allows my dad to lock her out of the master bedroom with the standard privacy lock (which she can open if needed). My older brother has decided he is going to install the keyed entry lock over my mother's objections because he's "doing as he was told (by our father)". My brother tells my mother that she "isn't in charge of Daddy" even if she is his wife of 62 years. I have told my brother that he is not installing a keyed lock because (1) the competent home owner/parent has said no and (2) it could potential create a death trap. My parents are both old enough that they do not easily adapt to new devices and I'm not sure either one could open a new keyed lock in an emergency. If that door is keyed locked, then my mother might not be able to get into the bedroom and wake my father up if the fire alarm went off. Of get to him if she heard him fall or he called out for her help. On the other hand, I don't have those concerns about operating the basic privacy locks that has been installed since they moved into the house in 1963. The entire family except for my older brother (who has Daddy's power of attorney signed well after the dementia was documented) agrees Daddy has not really be competent for some time. My brother tells my Mom that Daddy is fine and she is the one who's having problems and incompetent (no one including my mother's physician agrees with that). My mother does have some short term memory issues that her doctor states are a combination of normal aging, a medication she is taking, and the stress she is under caring for my father. She may need a little more time to consider and make her decisions, but she is capable of understanding her options and making her choices. I see my responsibility as supporting my parents to be as independent as they wish to be for as possible for as long. With their permissions, I installed a security system in their home so there is a monitored fire alarm (I was concerned they wouldn't wake up with the normal fire detectors) and a medical panic button. I guess I have two issues - (1) my brother seems to think he's power of attorney has made him :in charge of" our parents and (2) I think I have a responsibility to oppose creating potential death traps in our parents' home. I told my brother tonight that I would call the police if he starting changing the lock over our mother's direction and request Daddy be taken to the hospital for an evaluation. He backed off for now but it may just be to regroup. My mother asked me to come to the house and deal with my brother tonight as he is very verbally and emotionally abusive to my mother when she opposes anything he wants. My brother told our father that I would not let the lock be installed and that I was telling Daddy what he could do in his house now and got Daddy even more upset. It doesn't seem to occur to my brother that he's trying to tell our mother what she can do in her own home. I feel I need to support my mother - its her husband and her home - particularly when she directly asks. I don't want to get into power plays in the family, but I feel I can't let safety issues go either. Did I go too far?