@MarianT sounds hood, but to be honest, I am not sure if you can mentor rock climbing either. I was kinda mouth-spewing ideas. I love the endless story possibilities this dynasty challenge.
A sim with Level 10 Rock Climbing can "Coach rock climbing" and "offer tips" to other sims. I'd learned this from a video but Carl's Guide offers the same info.
Here's the link the Rock Climbing skill guide:
https://www.carls-sims-4-guide.com/skills/snowyescape/rockclimbing/@MarianT I'm going to go start a new save now to test. My understanding is that only the excursion leader and other household members require the appropriate rock climbing skill, but not NPCs.
I'll report back with confirmation soon.
Edited to add:
Excursion members: I had a YA sim with L7 Rock Climbing skill invite his (same household) wife and 3 NPC coworkers on an excursion with my sim as the leader.
His wife never arrived, perhaps because she has zero Rock Climbing skill.
The NPCs climbed autonomously; one of them left after the first rock wall, which caused the excursion to fail (the entire team couldn't "move on").
Maybe because it was a work day?
Later, I added the same 3 NPCs to my sim's household and none of them had any Rock Climbing skill.
"Coach Rock Climbing": The level 10 perk "Coach rock climbing" is a friendly interaction that didn't cause the other sim to acquire the Rock Climbing skill.
After the sim acquired Rock Climbing 1, being "coached" didn't increase her level at all.
TLDR: Only your hero (and any other household members, I assume) require sufficient Rock Climbing skill; team member NPCs will climb autonomously with success.
"Coach rock climbing" is simply a social interaction and doesn't work like the Mentor interaction. So disappointing!