My advice would be for the 4 of you to decide on a pace that is doable for everyone and stick with it. In any group there are bound to be faster and slower hikers but as long as everyone is on the same page about the pace of the hike then there shouldn’t be any issues. I’ve also found while hiking with a group that you shouldn’t expect to be actually hiking together the entire time. It’s ok (and I prefer) to split up every now and then but designate meeting points throughout the day and your camp at night.
Also you might want to ease into the trail, don’t try to do too many miles each day, especially at the beginning.
Otherwise just relax and enjoy it. The JMT is one of the most spectacular and beautiful places in the world and hiking it is an experience that will change your life for the better! Have fun out there and happy hiking!
Garrett