Actually I validated above point and the answer is YES, meaning one reviewer is enough to review any user's admin-role.
However, one interesting thing I realized is, the access-review that I configured was with Auto apply results to resource = OFF
Hence I did not expect the reviewers remove-access OR approve-access decision automatically applied.
And indeed NO change happen in the end-users role.
So my question is, how to apply the reviewer's decision.
I was hoping that there would be "APPLY" button where the AUTHOR/CREATOR of this access-review will go and apply the reviewer's choice.
However, I could not find such mechanism on AAD portal.
Appreciate your help !!!!