Good question. I’m not sure I know or could find the best people.
They might very likely not be celebrities or well-known, and they would very likely not be politicians. I would look for the wisest people with the most insight and benevolence towards the Earth as a whole, and to cover a wide range of perspectives.
Celebrities that come to mind:
Dalai Lama
Noam Chomsky
Jane Goodall
Stephen Hawking
Marshall Rosenberg
But of those, the Dalai Lama is the only one I think is likely to be one of the best choices available.
Also I naturally tend to know of Western people, and I would want representatives from around the world, certainly someone from Africa and someone from Europe.
With seven people, I would probably want four to be women. Certainly not more than three cis males.
I would also want a couple more environmental experts of different types, probably a climate scientist, and a ocean expert, although it would also do to have people who will seek the knowledge and guidance of the experts.
There should be at least one representative of ancient people, such as someone from the Kogi .