Everyone can still use the same Apple ID. What you need to do is go into – “Settings” , “Messages”, “Receive At”, and add a different Email for each user for where they can be reached for messages at. Once you have added a new Email to each device delete the original Email that was there which should have been the same as your Apple ID. Then when you send a new message, send the message to the Email for that person that was just added to their iPhone. There is no need for each family member to create their own Apple ID just to use iMessage. Each family member would only need to create their own Apple ID if everyone wanted to use iCloud and not have all family members data, contacts, calendars, etc sync together. If you are also using FaceTime between iPhones do the the same thing in the FaceTime settings.
Hope this helps.
Finally got an answer to this minor vexing question
Joel Vincent 