No, merging or migrating Twilio accounts is not available. It is also not possible to convert a parent account to a subaccount or vice versa.
However, we can transfer any active numbers and positive account balance over to the new account, and close the old account if needed. Please contact the Twilio Support team to help complete these changes.
For full details on how to request this change, see Moving Twilio phone numbers to another Twilio Account.
Note: We do not currently transfer any users, payment methods, subaccounts, existing phone number configurations or applications (like SMS, Voice, Chat, etc) or regulatory bundles, addresses, or Trusthub and Whatsapp registrations. You will need to recreate/re-register under the new account.