I got a reservation for late August hiking out of Road's End in Kings Canyon online. Told a buddy and he insisted on coming with me, so I had to submit another request for 2 hikers instead of one. Explained what I was doing in the email. They apparently understood, but didn't contact me, and gave me a reservation for 2. Paid online. We'll see what happens next.
Yes you can always add people to your wilderness permit if there’s available quota.
“ 4. I already have a reservation. Can I add another person? You can add another person to your wilderness permit reservation for an additional fee as long as space is still available for that trailhead. If space is no longer available for that trailhead, you can try to change your reservation to another date or another trailhead (as long as space is available).”