> Are bear canister available @ the Lone Pine ranger station? If so, how much are they?

You can rent canisters from the Visitor Center where you pick up your permits. Also Whitney Portal Store, and maybe the Hostel, too. I think they're $2 per day.

From the Orientation Notes: http://www.whitneyzone.com/wz/ubbthreads.php/topics/88/Orientation_Notes_for_Whitney_#C7

> How many bear canisters would you recommend for a group of 7 for an overnight trip?

You only need to store the next day's food in the canister, so maybe 2.

> do you leave tents/packs unzipped to prevent marmot/other critter damage?

That is what I would do, with any remaining snacks, etc, in the canisters.

> The group jokes that I am the worry wart/mother of the group.

Mother Hens are needed to take care of all the details. People who just show up sometimes get lucky and make it to the top. They're the ones who have the crazy stories to tell.

> what temperatures would you expect for a mid-August overnighter,

Watch the NOAA weather forecast closely -- see the Summit Weather link on the Mt Whitney Weather page. At sunrise, it is often frosty at the summit. Then, if there is a wind chill... Be prepared!