I have read that it takes between 2 and 3 weeks for a sea level body to acclimatize. I suggest you investigate bringing along Diamox for the group. I use (as needed) 1/4 of a 250 mg pill per every 3-4 hours. Diamox is a mild diuretic that counteracts the edema that is the hallmark of AMS/HAPE/HACE. Mild side effects include more urinating and sometimes a tinny taste to carbonated drinks.
The altitude issue should be taken very seriously, not only for success of trip but for safety. A guy died last year at 10k with HAPE attempting Williamson I believe; he had come from Philly and headed up same day.
