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The 2 without should get some Scottish Winter experience beforehand
And some experience above 4,000m too. Scottish winter skills are not enough to get you up there if you're not ok with the altitude. Mont Blanc normal route is roughly 2 x Snowdons in less than a day with ~40% less oxygen available to you.
Most of the "tourist" packages for Mont Blanc factor in a week of altitude exposure beforehand. That sort of package is well worth considering imo. Gives you quite a bit of experience before the big day.
The 2 without should get some Scottish Winter experience beforehand