Tourism visa refused for my brother

I need you help please.I made a tourism visa for my mother and brother to visit me in the UK,my mother was given a visa while my brother not.My brother has learning difficulties,so all his money which he inherited after the death of his father is under the control of our mother due to my brother medical condition.We attached a medical report stating that he should be always accompanied by his mother as she is his only sponsor.the refusal letter mentioned that the visa officer wasn’t convinced that my brother will return back to his home country.The officer needs more information About his personal circumstances that convince the officer he will return back to his home country.Also,the officer mentioned that the report was not dated.Any ideas what documents should we provide!?
Any one has previous experience about dealing with issues regarding people with learning difficulties or mental issues??
Thanks in advance