Will these work in Artic temps?

I wore mine as a base layer in Alaska during the summer where temps dropped into the 30’s. I guess it depends on what your other layers will be. But they worked for me as expected.

Is the top also 250 merino wool?

Both the top and bottoms are made of the same material. It has been below zero here and they kept me warm running errands yesterday

Will this merino wool set protect me from the cold during my trip to the mountains?

It won't hurt. But it depends on a lot of other factors- how well do you deal with cold weather, how cold will it be where you are, what other kinds of layers will you have with you, etc. No one item can protect you in all circumstances- but I wore these as a base layer through last winter, with cold ranging down to the teens and 20's, and I don't like cold weather. It helped a lot as a base layer for sure, they are very decent quality wool underwear. I liked them enough that I bought a second set. Hope that helps.

The lifetime warranty lasts 60 days?

The “Lifetime” Warranty statement is confusing. It’s good you brought that to attention. Perhaps contacting Merino Tech. would be best for Warranty specifics.