Thank you very much, Jot18 and MikeE, for the additional pointers.
Yes, makes sense to apply for the reununciation certificate and visa at the same time.
And, no, not planning to use my wife's Indian passport. I was just noting that it is not physically cancelled (that is, it is not physically clipped/stamped as null yet).
We will try for the 5-year tourist e-visa. Assuming we get that in time, and are able to travel to India, the plan will be to apply for the OCI once we get back from India.
Thanks again for your help.