From twilio docs
“If you send multiple messages at once from a single Twilio sender (number or Alphanumeric Sender ID), Twilio will queue them up for delivery. Your messages may experience differing rate limits based on the sender you are using. For messages from a US or Canada long code number, the limit is one message segment per second (MPS). If you're sending messages from a non-US or Canada long code number, or an Alphanumeric Sender ID, the upper limit is 10 MPS.”
Your best bet would be https://www.twilio.com/docs/messaging/services/services-send-messages or multiple twilio accs