"For a while now any replies to any email are being sent from my wifes account even though the original email was addressed to me or my son."
I'm puzzled how this has started happening of its own accord. Anyhow, the first place to check is in the properties section for each mail account in Outlook. Start with the abc1@ account and make sure the in the "E-mail Address" section it's showing abc1@. Do the same for all the other mail accounts.
What should then happen is that the e-mail address used in the reply is the same as the original e-mail and you should no longer need to specify it manually.
If that doesn't work then it'll help if you specify the version of MS Outlook you're running.