Well, first off, congratulations for getting a group of friends to hike the Wonderland Trail. You picked a good time of year to hike the mountain, late July and early August often is the driest time in this part of the world.
I looked over your gear list - it looks pretty good to me.
I can comment on a couple of things:
The NeoAir should be fine on its own. I don't think you will need anything more unless we have another late and cold spring (like we had this past season). As a result, the snow didn't melt out until four or five weeks late. But seriously, it's usually a very nice time of year to be here.
As for your tent, I would likely opt for the Shangri La. I have a Tarptent, and if you are sharing it with another person, it can be a bit of a challenge in the event you encounter cooler / wet weather. Though this is unlikely in late July, it certainly isn't unheard of - the sagging of silnylon as a result of high humidity/rain makes keeping a taut pitch tougher. The net result? The walls will have a tendency to sag a bit and as a result can come in contact with the sides of your sleeping bag. If this happens, you are going to have a wet bag. But, and there is always a but - depending on the season it can be buggy in late July. SO a bug net would be recommended especially when and if you camp at lower elevations. Plus, I think the real estate might come in handy in a bigger tent. I haven't had issues with critters - just mosquitoes.
On clothes - well, let me just preface everything by saying I can wear the same clothes day after day while hiking. BUT I do like to carry seperate sleepwear (including sleep socks) only because I don't want to go to bed in damp/wet clothes and socks. I wear that stuff exclusively when sleeping except for the last day, when I will walk out in that stuff if the weather warrants it.
The temps on the mountain can vary quite a bit depending on the weather. This year we had unseasonably cool summer - in the mountains because of all the snow it didn't heat up that much. THe days were nice but it was definitely cool in the evenings. I would go with the long underwear. If I had zip-off pants, I'd use those exclusively (and not sleep in them). Or I you prefer shorts, go with the lightweight shorts and hike in those exclusively. I wouldn't carry both necessarily. You are going to get dirty. You are going to sweat. You could see some snow.
If you want, you could always cache extra clothes. How so? Do you plan to make use of the ranger stations along the way to cache food/fuel? If so, you would only need to carry 3-4 days worth of supplies at the most at any time. You will need to plan this out and of course, it does depend upon the sites you draw for your permit. You can mail food/gear ahead to selected stations - we drove as I live within an hour of the mountain. You could put an extra shirt or other clothes into one of your caches.
Here you can find info about the food caches.
The phone won't be of much use on the mountain except for a couple of spots. I did get a signal along the west side of the mountain for a short while.
Finally, fires are prohibited pretty much everywhere along the trail. Stoves are permitted, but make sure you read up on the rules regarding sending fuel through the mail.
Finally, send in multiple permit requests! And pick good spots. Are you going for group sites or just individual sites? In most of the individual sites, you can fit two tents. The group sites do have the advantage of some shelters.
Among the many campsites I'd recommend reserving are:
Summerland - Follow the trail out a bit ...the ones further back are the best
Indian Bar (if you do choose the individual sites you will be tempted to camp near the river...For a MUCH warmer experience, climb up towards the latrine. It goes back a fair distance but up here it is MUCH, MUCH warmer. The cold air that sinks from the mountain side will be below you.)
Klapatche Park - my favorite spot to camp on the West Side
AVOID camping at MOWICH LAKE at at all costs - it is serviced by a road and is terrible place to camp. It will full with people.
Oh, and do take the Spray Park Alternative rather than follow the traditional route of the Wonderland Trail - the scenery is WAYYYY better. Not even close.