Message reply on Mac goes to wrong person 3 people at my office send me messages from their iOS device. If I read and reply from my iOS device, all works well. If I read and reply from my Mac, the replies get mixed and and the wrong person receives it. I have each set up in my Contacts with unique mobile numbers, but identical work numbers.

Any ideas? I have resorted to deleting the coworker who receives the messages from my iPhone and laptop contacts, but that doesn't feel like a long-term solution. Firing him does, I'll look into that for sure...
At the top of the conversation of the Messages app the contact should be listed under the To: header. You can use the arrow by the name to select more details and change which number you are replying to.

As an alternative you could delete their work numbers, or put it in the notes section of the contact to prevent Messages from mixing them up.

It's best to delete the conversation and start a new one after making changes like these to make sure that messages is using the proper contact info.