this seems to be a sequel of birth asphyxia
or hypoxic ischemic encephalopathy
in medical terms.
in this there is lack of blood supply and hence oxygen
supply to the vital organs of our body just after birth because of lack of immediate crying leading to their dysfunction which in case of brain may be very severe as brain can't stand lack of oxygen for long.
the best way of dealing with this kind oof developmental delay should be proper care and physicam rehabilitation
that should have started very early in infancy as soon as the signs of sequel is apparent.
but its never too late to start anything.
first you should visit a pediatrician
who can do a thorough physical examination with a proper history to evaluate for neurological deficits and other issues like seizures if any. and can suggest some medicines as required. he will also refer you to some physiotherapy
centre for proper rehabilitation.
the management is multidisciplinary and is very much demanding and you will have to start with full devotion. i wont say it will make your brother just like any other person of his age group, but it can surely make him self sufficient as far as personal care is concerned.
hope i ve guided you properly
good luck and wish your brother a healthy life.
Dr. Amit Kumar