You must get him to ask for more support from Social serives.
There are a variety of day care options from a 1-1 at home for a few hours to going to a day centre once or twice a week. She shouldn't be home alone if he is working full time she needs 24 hour care.
He needs to ask for a carers assessment which will look at his needs and arrange the support for his mother according to this. He needs to 'shout' and keep on about what he expects others wise it is easy to get over looked.