Anyone with a younger sib that's stressed out by older one applying?

Yes, pre-meds will face GPA stress throughout college (unless they decide to stop being pre-med).

However, if the younger kid is not aiming for something hyper-competitive like medical school, then you may want to make sure he knows that not everything is hyper-competitive like medical school.

In all fairness, the syllabus for UCB CS 61A does give warning that it can be hard for those with less prior experience or previous course work:

https://cs61a.org/articles/about.html