IPhone – Why are the iMessages being sent through the Apple ID

iMessage isn't designed to work with just one Apple ID. Instead of having all the iPhones and iPad on one Apple ID, it will be necessary to set up additional Apple IDs for the different users.

When you setup an iOS device and put in your Apple ID, it provisions ALL such services to that Apple ID. Go into Settings on each device (under Messages and FaceTime) and remove the Apple ID. Replace the Apple ID with a new Apple ID unique to each user. Here is a guide on creating new iCloud accounts for this purpose.

Better yet, provision each account completely with its own Apple ID. If a person wants to download an already-purchased app or song from a different account, you can temporarily change accounts in iTunes or App Store.

The easy way to fix this is to look at the contact card. (Assuming the issue is on your side of the sending)

You could temporarily move the phone numbers to the notes section and delete them. Then sending a message has to go via iMessage if their email is registered for iMessage.

If not, just add back their mobile number and initiate an iMessage to them from the address book/contact card view. Tap the chat bubble next to their email or phone to initiate an iMessage transmission.

It's often required to start a new thread if you keep sending to the wrong email/mobile number since Messages wants to hold on to the way the last message was sent and not jump back to iMessage if the other person's AppleID hasn't claimed the mobile number, so keep in mind the problem might be on the other person's account - not your address book or contacts.