a simple question can we add multiple username in bitcoin config ?
to access rpc and assigm them seprate wallets
So you want to develop a web wallet where users don't need to download a full blockchain with a separate wallet and want to manage them on a pooled single wallet with your node?
If it's for the RPC server then no it doesn't support multiple users you will need to develop software where you can track sent/received to each user and make sure that they can only spend BTC that belongs to their wallet address.
Or else you will need separate full nodes for each user but this will require more resources.
Since you mentioned you are planning to develop a marketplace why not use BTCpayserver for your users? It has a feature called "BTCPay Server Wallet".
You can find more details about this here
https://docs.btcpayserver.org/Wallet/Don't worry about hosting BTCpayserver you can run it with your PC and it requires a node but you don't need to download the entire blockchain, the minimum pruned is around 5GB according to their documentation.