The decision to discontinue or taper antiepileptic medication is made on an individual basis after carefully weighing the risk of seizure
recurrence and benefits of drug withdrawal.
There is no certain way to predict who will remain seizure free or who will have a recurrence after stopping medications.
Some of the risk factors which can increase the chances of a recurrence are people with tonic clonic seizures requiring more than one antiepileptic drug,family history of seizures,having multiple type of seizures or having an abnormal EEG etc. Some seizure syndromes like Juvenile myoclonic epilepsy
have a higher chance of recurrence.
Keeping all these factors in mind you can discuss this matter with your treating doctor or a Neurologist
. Depending on the Seizure type your brother is having and the other risk factors your doctor will be able to advise you appropriately about how and when to go about tapering the medications.
Hope this helps!