Can anyone tell me how many bear boxes there are in a group camping site at Whitney Portal campground?
You will probably not find any bear box that is empty. Normal protocol is to share space with the other users. Many overnight hikers will leave extra food in the boxes (removed from their cars), sometimes for days. I would plan on using several boxes to accomodate a group your size.
As mentioned above, four boxes in the Portal Campground sounds about right. If memory serves me, there is another 2 (or 4?) in the overflow parking lot that have less demand. Also, I believe there is a pair of boxes on the left as you approach the area. Someone with a sharper memory may be able to provide more help (I am sure Mr. Bruin knows

).