So that's what, 150-200 people who are going to be eating this turkey, right? That's a pretty hefty cook. In the interest of making it as simple, foolproof and SAFE as possible, I'd definitely spatchcock or split them, and I'd definitely brine them. Yes, you CAN cook a turkey to moist and tender perfection without brining it. So why brine? It's an insurance policy. You're gonna have a whole shed load of turkeys going at once, and nailing the perfect temperature so it's safely done and not dried out requires precise timing and temperature control. With a brined bird, the sweet spot between done and dry is a lot wider range. You'll be able to take them to 175˚ in the breast (which you'll want to do. People will scream bloody murder if they see pink in poultry, even if it temps perfectly safe) and still have a moist, presentable product. The skin? This is a big operation with a lot of people, and it's going to require some compromise. Skin that's a little rubbery isn't the end of the world I'm guessing it's going to be sliced and held in chafers, so the skin won't really be an issue anyway. If it's too tough, chuck it.
This isn't Thanksgiving with the family, this is a foodservice operation. There's a reason restaurant and institutional food is on one level, and home cooked food is on another. It's just not practical to go to the lengths we go to at home when preparing large quantities of food, and sometimes it's just not safe. I'm not saying you can't make really good food on a large scale, I'm just saying the approach has to be different.
By the way, spatchcocking that many turkeys is gonna wear out your hands, your knife and/or your shears. Get a new $15 electric knife and a spare set of blades and it'll go a whole lot faster. The reason I say a new knife is you want the blades to be as sharp as possible, and going through that much bone will likely trash them by the end. A reciprocating saw will work too, just make sure it's clean and you're using an unpainted blade.