If you are on a team you will only need 1 twilio user account and phone number.
A team can share a Twilio account in the CRM, just by setting the type to company account when creating it.
The user that sets it up will however be assigned as the owner, but all other company colleagues can use the number to send messages.
If a response comes in, the response will be sent to the cell number of the user that sent the message not to everyone. If a response came in and the last user who contacted the lead was not the main agent, then the response will go to that user only if it came within 7 days, if not it will be sent o the main agent.
If a call is made to the number for a lead the user that sent the last message to that lead should get the call (forwarded to his cell). If no cell is entered the owner will be called.
In order to ensure that the twilio account is setup properly, please make sure that Company Account is selected and not Personal.