Advice on how to manage mums increasing dementia like symptoms

I am so sorry Elsine, it is so hard when hey are not compliant.
She will come around eventually when she realises your brother has his own life and may leave if she does not play ball. I would imagine the GP would have done a mini test which is all they do as he has asked for an Xray and Blood test, which will guide him as to what to do next. But even if you get a diagnoses there is little you can do whilst she can still decide for herself. You can only give her the choices if she declines, she will soon realise she is not coping well without your brother's help. Could you introduce a carers as your friend when you are there next weekend (provided you can get one that quickly) hopefully your mother will like her and let her come for a cuppa again and again and eventually it may work. You have tube devious at times to make work. Could you book her a holiday (respite) for a week or two to see how she enjoys that? I would not worry too much about your mother being cross, she will over herself. She will be even more cross if your brother decides to leave and she is on her own without help, then she has to eventually accept some. Some times we have to be tough and "unkind" to be kind and do what is in their best interest. Which after all is what we undertake to do when we accept the POA duties. Good luck.