when you go in first shell fit your self, don't go buy any of the sizing listed other then the bsl, which should be printed on the one of the sides of the heel lug, 26/265 are right around 305, 27/275 are usualy 315-320 off the top of my head, so any way the shell fit, take the liner out put your foot in the shell, move your foot so your toes are touching the front of the boot, lean forward, keeping your toes touchig the front and get your fingers between your heel and the back of the boot, there should be no more then two finger widths between the boot and your heel, two fingers is ideal, racers tend to go one. you will be ok at 3/2 - 2,
so find the shell size that works for you this is very important.
Then put the liner back in the boot, and put your foot in, also it is a good idea to have a thin pair of ski socks on, like you would for skiing. before standing up buckle the boot, now stand up and flex the boot forward while holding the flex alternate using the top two buckles to pull your foot back into the heel pocket. then latch the insole buckle on the first setting that will hold it, then thighten the toe buckle, and lastly cinch down the power strap
When you stand stright up your toes need to be touching the end of the boot, when you flex forward they should come back a little. The boot should feel like a tight glove all around your foot especialy in the ankle, lower leg and fore foot. If it is crushing (not just tight and snug) your fore foot the boot is in all probability too narow and you need to go to a wider boot, if it is not very snug the boot is too wide and you need a narrower boot. Once you find the fit that works best for you, stick to that line of boots, not brand, untill you find the flex that works for you. so Salomon Impact, Technica Vento, Lange Fluid, ect, Keep in mind however that when you start hitting the high end boots in free ride series the sheel usualy changes to a plug shell, expamples: Nordica Supper Charger, and the Technica Agent.
I can't garuenty you will get good results with that but for the most part it is how we do initial fitting, Its a fairly simple method that usually gets good results,
All and all remember that smaller is better then bigger when it comes to boots, be ready to spend more on boots, they are the most important part of your ski equipment. Also the shell size is the most important part of what I said except for what I am about to say.
If your family does go on a ski trip to some resort at say christmass, or presedents day, resort vilages allways have really damn good boot fitters at them, look online to find one with a good reputation, there is a pretty good list floating around TGR. Also be ready to drive in your area, Yesterday I had a guy who drove from Bend OR to Seattle WA to get fit because quite simply it is worth it to get a good fit. There really is nothing like a good boot fit.