You would need to purchase an EWR-MEX ticket and a separate MEX-NRT-EWR ticket (presumably on NH). You would have to hope that NH sees that second ticket as a NRT transit and you are at its mercy. If it goes wrong, you are stuck in MEX. Same problem for you if your xEWR flight goes sideways and you no show for your second ticket.

In these times with limited options, I see traveling on separate tickets and on complex routings as risky. If it goes wrong, your wife is left standing at NRT. Moreover, she presumably needs to be ticketed on NH as well if you are to accompany her.

If your return to the US is on or after the 26th, both of you will require negative tests.