Hello Lesley, you are in such a terrible situation there, I completely sympathise with you and the family. When you found your Mum in the poor state you described, would you not have been able to contact social services about it as a neglect case? It would put the blame on him, neglect of that type is serious abuse. I know your Mum wouldn't have wanted that to happen, but it would have bought the situation out into the open.
If your Mum is classified as having dimentia (horrible word), you could contest any will she may have made during that time with him as he would be seen to have taken advantage of the situation. Perhaps your Mums neighbours would back you, as they saw his neglect first hand. Report it to your Mums GP and yours too, get it on file..
Would your Mum consider a little holiday with you at your house? It might open her horizons a bit and perhaps she might understand a little that she is safer and cared for by family more than she is with him.
Have you tried talking to your GP, or a professional about this? There must be something you can do to get your Mum back.
I don't know what we can do about our situation, our relative is not interested in making any changes, he has fallen for their trickery completely and feels like the sun shines from their nether regions. Although he has been an easy target for them after the loss of his wife and sister, he IS of 'sound mind' and therefore its his choice. They have cleverley worked on him for some time and are not prepared to have it spoiled by his family.
It breaks our hearts, so I cant imagine how you must be feeling.
THINKING OF YOU , SUSE.