A friend (or 2 or 3, but counting on 1) and myself will be butchering 12-13, 3.5 - 4 month old cockerels of various breeds at the end of the month.
At that age the cockerels shouldn't be too hard to skin except for the wings. If you wait another month the connective tissue, including the tissue that holds skin to the carcass, become more of a problem. Wings are a pain anyway. I use poultry shears to clip off the wing tip and toss it, I don't consider it worth it. I use a knife to cut off where flight feathers were but it still takes a lot of strength to pull that skin off. I had not thought of scalding and plucking wings after you cut them off. It will be interesting to heart how that worked.
I’ve got a cheap tent, and can hook up a box fan or something.
Good, you need to be in the shade, both for comfort and to avoid sunburn. It's probably going to be in the 90's so a fan isn't a bad idea either.
It would be tedious/inefficient to do just one at a time and process all the way through, so was considering killing several, then sitting down to skin and part.
I do it by myself and just do one at a time all the way through. I also part them which slows it down. I get into a system and rhythm to try to avoid a lot of wasted motion and wait time but it is kind of slow. The only overlap is that I kill one after I've finished parting one and use the time for it to stop moving around to put the meat away and clean up for the next one. With more than one person an assembly line approach could speed you up as you gain expertise with a certain task. You'll have to work that part out depending on who shows up.
From a bacteria standpoint I don't know how long you can wait to clean them and get them cooled off in that kind of weather. Those temperatures are prime conditions for bacteria to multiply. You don't want rigor mortis to start setting up either, that would make it hard to butcher them. I don't have a safe time.
and how can we, keep flies and such away from the carcasses before we get to process them?
Flies haven't been a problem for me. I hardly ever see any. When I do they seem to go to the bucket where I'm putting the offal. I think they are drawn by smell to aging meat and such instead of an extremely fresh kill. Maybe have some mosquito netting or something like a towel handy so you can cover the carcasses until you get to it if it becomes a problem.
Are there any other things I need to consider about butchering in the heat I might not think about?
Do what you can ahead of time. You are going to be tired. If you are going to bury the offal, dig the hole the day before. Do as much set-up as you can the day before. Gather your equipment, sharpen knives, if you need ice get it the day before.
Take care of yourself. Drink plenty of water, take a break if you need to, don't sunburn. You are going to be tired. That can lead to carelessness around sharp implements.
You want to get everything done that you can while your crew is there, I would. But if you get in a bind, you might consider aging the carcass after the bird is skinned and gutted to get past rigor mortis before you finish parting it. You may be able to part it in your air conditioned kitchen but clear things out so it is easy to sanitize the work area afterwards. That would not work very well for me because of the way I clean it and age it, but maybe for you.
Good luck and let us know how it goes.