Sundae, my uncle has dementia and alzheimers. He's quite violent now and in full time care because my aunt can't care for him.
It's a very difficult journey for any family. Frustrating, frightening and just plain old scary. I feel really sorry for you and your Mum having to deal with it every day. Must be hard. and very painful to watch.
Don't worry about sexo. He's just being his usual self. What else can you expect of anyone?