There isn't to be any holding seats, and isn't advisable as people will get bent out of shape and judge you for doing so. As a parent of an ASD son and based on his needs..., my advice would be to board together and have some of your group sit directly in front of him. Our challenge with our son has always been his obsession with constantly playing with the seat tray, and bumping the seat in front. Knowing that, we always have one of our other kids sit in front of him and it certainly makes it a lot less stressful know that he's not bothering a stranger. Also putting him by the window vs the middle seat or aisle seat helps to shelter him from on lookers if he needs to hand flap, or make the odd unusual vocal sound. Snacks and an ipad work wonders for him. As previous posters have said SW boarding is fairly quick, and I don't think holding back is that big of a benefit. We have always found boarding together as a family is much less stressful, as we can work as a team managing our other kids, stroller and a couple carry on items. Also this way our son does not get upset if he sees his siblings leaving him in the terminal while they board. Pre-board has never worked for us as we are a family of 6, but may work for families of three, as stated. Airports and flying are definitely challenging for many kids on the spectrum.... Hope all goes well, and you have a great trip!!!