No. Nomination can be made account wise and not security wise. So you can nominate at the level of your demat account, not at the level of individual ISINs. What you can do is to create another demat account. Shares you want to nominate your brother keep in one account and your sister shares nomination keeps in another account. You can shift shares through off-market transfers. Once this is done then you can have appropriate nominations and the problem is solved.