You now seem to be fairly clear you're talking about the former, largely doable and indeed mostly implemented case.

Quite the reverse, actually. That "dynamic" environment hosted by a separate service is not nearly as significant as you portray it. The entire point of a meeting is for every observer to share the same experience.

Again, it is completely trivial for the underlying AI to recognize it has been asked to sit in on the same meeting, and act as the personal representative for each of 25 separate people.

If you're under the impression that there is a personal, private relationship between an individual and an AI instance, I suggest you disabuse yourself of that notion. If there is any distinction, it is only because the underlying AI has been instructed to schizophrenically simulate it.