> Our plan is to hope that there will be enough walk up permits available so we can change the permit to Whitney Portal to Cottonwood
You have another option: Ten Trail Crest exit permits are reserved for walk-in requests. I believe they are passed out, though, to the earliest walk-ins, even JMT hikers coming down from as far away as Devils Postpile. So there may not be 10 available.
However, consider asking for available Trail Crest exit permits across several days: your expected exit date, plus a day before and one after. You might be able to break the group up and exit different days, then gather again at Consultation Lk for the last night.
I sure hope you can get the right permits.