For those conditions, the only one of Tarptent's many excellent tents I'd consider is their Scarp 2 which is a 4-season tent. You'd also need the extra external pole, so you need to factor in the weight and price of that item (multiplied by 2, since it's a 2-person tent). (Their Moment DW with the external pole would also work, but that's a solo tent.) I still would go for Hilleberg or a similar 4-season mountaineering tent, though. (I am not familiar with other European makes so can't judge there, but I suggest that you investigate.)

I very much doubt that two 2-person tents would be lighter per person than one 4-person tent, assuming a similar degree of weather-resistance, but it is easier to find suitable sites for two smaller tents rather than one large one.

I agree with those above who say it isn't the tent that keeps you warm. Nylon walls don't insulate; they only block the wind. One thickness does just as well for that as two. In a double-wall tent, the inner tent has to "breathe" for ventilation, so has no coating and cannot be windproof. However, you need a 4-season tent both to hold up under the weight of snow accumulation and to block blowing snow (spindrift). A single wall tent requires quite a bit of open area (with netting) on the outside perimeter for ventilation, and that won't keep out high winds and blowing snow!

As you've noted, you need to keep the currency exchange rate and shipping cost in mind before deciding whether to buy in the US or closer to home.

Thanks, Tom, for finding that beautiful video! Too bad the view of the distant mountains was so fleeting! That definitely looks like a place for a 4-season mountaineering tent!