This sounds a really difficult situation @Crosscopgirl and I’m not sure it’s going to be easy to manage. I don’t really have personal experience of alcoholic dementia but a friend’s brother has it and I understand he flies into rages. I can understand you being intimidated.
Do you think your mum is safe living with him? I think I’d let her GP know what the situation is as if s/he thinks there might be a safeguarding issue they should know what action to take.
I’m sorry I can’t be more helpful. I know there is reference on the site to alcoholic dementia and korsakoffs so perhaps you will find something useful if you put these terms into the search bar at the top of the page.
Hopefully someone with experience of this will be along soon.
Plenty of people here to listen even if can’t advise or have any experience they are all very supportive .Thankyou for caring in your response. Ive just realised I can share this problem with others! Ongoing I have broad shoulders to carry this and Im thankful to have found others who will listen.