If one sibling has epilepsy( catamenial, diagnosed in late twenties) does the other sibling also has the risk to develop epilepsy? there is no family history of epilepsy or sizures than how common.is it for other siblings to have it?

Although 30-40 % of epilepsy is caused by genetic PREDISPOSITION, this does not mean that an isolated seizure disorder emerging in late twenties is indicative of a familial tendency. In my opinion, it is a waste of time, money, and medical resources to attempt to track down such vague genetic risks, at this point. But if concerns remain, you could seek neurological consultation for yourself.