Here is a photograph of the audience of SGA3 (as noted by Mateo Carmona).
Other photographs may be viewed from the homepage: https://agrothendieck.github.io/
Grothendieck is facing the audience. I recognise Dieudonne at the left in the front row, Mandelbrot (?) in the second row, Chevalley to the right of Mandelbrot, but no one else. (Corrections after comments.)
Does anyone recognise the others?