iMessage sending to the wrong contact

When I pen an iMessage to my daughter, using her iPhone number, from Messages on my iMac, everything looks good until I hit the Send button. At that point it changes the number from hers to her husbands, who has a completely different number. Additionally, the same problem occurs if she sends me an iMessage and I reply to it from my iMac, it will send the reply to her husbands number! Their respective Contacts entries have only their respective iPhone numbers in them. This ONLY happens when using iMessage on the iMac. It does not happen when I send her a message from my iPhone or iPad. This occurred in El Capitan and also occurs in Sierra. This only happens between these two contacts. Every other iMessage sent from my iMac goes to the correct contact. Anyone familiar with or have seen this problem? Any suggestions for fixing?