North, Everest, Wilder
Wilder ends with the popular -er sound as many surnames like Thatcher, Fletcher, & Parker do. Wilder seems to match your unintentional nature theme. Wilder sounds like he could be a handful, but adventurous and wild & free. Wilder could also be shortened to the tamer Will if needed.
I think you have a lot of options with a sibset like North + Everest. Definitely an intriguing family of little boys, in my opinion.
Beau/ Boden/ Bowen
Ok, with Joyce, I'd avoid names ending in -s or -j. Also, 2+ syllable names may flow better.
Sorry for any repeats...
Equinox, nn Knox
Huron (people use Hudson, so why not?)
Caelum (Kai lum, Latin for sky and a constellation)
Leif (some pronounce it Layf, others say Leaf)
Mavi (Blue in Turkish)
Arran (a Scottish place name)
Firth (Bay of Firth)
I think that what you are saying is that you want something aspirational, cool, maybe slightly 'badass' without being overtly nature-oriented and something that will keep your sibset from straying over to a caricature of toughness (Max and Steele).
I'd look to surnames. How about North, Everest and....
Pike (though this does have the mountain theme)
I can also see geographic names working, but I'd avoid those that evoke the American West.....I think Bryce or Phoenix might take you back to the "outdoorsman" theme you want to avoid. Maybe:
I can also see some of the less trendy occupational names working:
When I think North and Everest, it makes me think 'high up, on top of the world.'
I like the suggestions that also hint at being the same way, for different reasons...
I replied under the sibling names forum, but I will add my suggestions here too:
North and Everest are really cool! For a brother I really like the suggestions of Orion and Wilder.
Of the names suggested my favorites are Aspen and Wilder.