Building on what Fishmonger wrote, you should be able to get 7 days of food into a canister if you make smart choices. You can also carry your first day's food outside the canister because you will be eating it. That makes for an 8-day "range". From Muir Trail Ranch, it's about 110 miles to Whitney Portal. So that's 14 miles per day, an "average" pace for a JMT hiker. Your pace will be dictated by the high passes, and that's about right.
Not sure what guidebook you're using, but the bible is by
Elizabeth Wenk, New 5th Edition Coincidently, I just mailed my resupply to
MTR today. It's $65 but worth it. Pack some luxury fiesta items and enjoy the hot springs across the river. It's a great midpoint break. The gang from "Mile, Mile and a Half" stayed there. It's on Netflix now.
Cool JMT Movie You can also resupply at Tuolumne Meadows and Red's Meadow to keep your food weight down. These are great stopovers anyway. Same with VVR, but MTR is just a little closer to the finish line.
Remember, the group should be getting stronger and more acclimated over time. But most importantly, PACK WEIGHT will control your pace. If you have heavy packs, then plan on resupplying somehow between MTR or VVR and the finish line, as described by Fishmonger or in a guidebook. That means either a long round trip to town, or paying a packer to deliver along the trail. Best bet is probably a packer drop at Charlotte Lake. Since you have a group, the cost can be shared more economically.
Although canisters are not "required" until your reach Pinchot Pass, there are plenty of bears along the way, especially if you camp at the usual spots. On the other hand, there are bear boxes at strategic locations, but they might be full. Alternatively, consider an Ursack to get some extra food through this area where a canister is not required, but bears are known to be a problem.
Ursack 7 ounces Happy Trails, eh.
