NRIs need Trading, Demat and Bank Account to trade/invest in India. Technically all these 3 accounts can be opened with different organizations. But this results in operational challenges.
It is recommended to open all 3 or at least 2 accounts (trading and demat account) with one broker/bank.
The most convenient way is to open 3-in-1 account with a bank which includes all 3 accounts. These accounts are integrated well to offer a seamless trading experience to NRIs. But the brokerages charged by the 3-in-1 account are very high.
For frequent traders, it is recommended to open trading and demat account with a discount stock broker (i.e. Zerodha, ProStocks) and bank account with any bank (i.e. HDFC, ICICI). This reduces the cost of trading.