RE: switchbacks. i am not sure about your comfort level moving over snow and ice (or the teenagers that will be with you). if *i* were going back on the July 17th, *i* would be comfortable leaving the ice axe in the car and just using crampons (if needed) and trekking poles to go up the switchbacks. please note: i am talking about me and my comfort level of being on snow. in the winter i am ski instructor/coach and so my comfort level might be different than other folks.
RE: the trail is very well marked and melted out below Trail Meadows. it started getting light around 4:30am-4:45am at which point i stopped using my headlamp as i prefer to hike by natural light whenever possible. so i don't think you should have any problem with getting lost in the dark. hiking by headlamps gives some folks "tunnel vision" since they only "see" what is lit up by their head lamp. Just make sure you look around!
RE: stream crossings. they were all fine... at least for us. definitely utilize trekking poles for balance as you pick your way across the rocks to cross them. i am not sure if rivers and creeks have peaked for that area.... i know i was talking to some rafting friends yesterday, and rivers around me in N. Tahoe peaked this past week.
RE: food. this is a personal thing... and what works for your stomach. i brought 1 1/2 bagel sandwiches with cream cheese and salami; home made gorp with nuts, pretzels, raisins, m&m's, banana chips, cheerios; a tube of Pringles potato chips; a couple packs of Clif shot blocks and 2 clif bars. i am sure jerky would work for calories and candy bars too (although you might want the kids to think about Clif bars or shot bloks or something along those lines.) oranges would normally be great, except they weigh alot since they are mostly water and you would additionally have to pack out the peels. again it is a matter of preference, because my wife loves having fruit on hikes and doesn't mind the extra weight.
RE: water. i know you didn't ask about it, but..... i had 2 water bottles or 2Ls and filled them up as needed and used purifying tablets... i don't bother with water filters, especially on an alpine hike like this. you might consider having 3Ls (at least for the hike from Trail Camp -> Trail Crest -> Summit and back. obviously it is at a higher altitude, you are in the sun, and i found myself drinking much more water on this part. just a thought....
in any case, hope that helps and good luck on your hike.