If you have a better phrasing, feel free to suggest it.
If I would have a suggestion that I am fully comfortable with, I would have written it above.
A possible phrasing might be: "minors, seniors, and people with physical or other dependencies".
The more I think about it, the more I think that rather than phrase it in any way, your suggestion of putting a high mandatory price tag on involuntary bumping (for example: the greater of $5,000 or the highest fare paid for that route within the last 30 days) would be a lot more effective. If it's left for bidding, there will always be someone willing to go off for the right price, and then there will be the vulnerable population that will just not be bumped.
ETA: I love the paint job on the airplane.