Twilio A2P 10DLC Starter Brand Registration for Sub-accounts users

I need help understanding the Twilio A2P registration for sub-accounts user. We have created all our users as a sub-account and that's how we managed them inside their individual phone numbers and their SMS and Call logs.

Now we would like to register them inside the twilio as this is requirement from Twilio to register all of our users. I want to know:

1. How can we register them as a sub-account. So we don't need to change all of our code and business logic for our users?
2. If we will register them as a sub-account all of sms and calls functionality will not be disturbed. Like everything will be managed through the webhooks of Twilio?

Thanks,