Status of nominee on expiry?

We have two joint accounts. One for demat and second for savings account with a nationalized bank.The accounts are having 3 joint holder.

I am a senior citizen and have nominated my family member in both the accounts.

Will the nominee be taken on record as account holder in the event I am no more.

How the nominee can ascertain his/her rights if other 2 joint holder play foul which is sure.

Thanks