I know a reaaaaalllllly good Canadian place. 
The adaptive winter sports at sunshine are run by a lovely lovely friend of mine who is actually a Brit, and my dd2 attends the downhill programme there. They offer whatever you want, completely tailored to individual abilities (it's a not for profit organisation). Very friendly, amazing, and staffed by great instructors and a whole host of volunteers for those who need more than 1-1 support. Also cross country skiing, and in the summer loads of activities too.
We actually moved here in no small part because of the opportunities they provide. we found them accidentally when we were looking for an instructor who could teach dd2, several years before we took the plunge and moved here ft.
Obviously, just getting to Canada racks up the prices enormously, (flights direct to Calgary, Alberta and book local accommodation) but if you ever manage to scrape the money together, you won't regret it. 
The organisation is here
They do fab 'family and friends' lessons as well, which might be perfect for all of your boys. As an aside, the website is a bit clunky at the mo as it's being overhauled, but do give me a shout if you want to ask anything or can't find the info you need.
If you do make it, give me a shout.
I can cover coffe, but not the cost of the flights, I'm afraid. 