I return to your original suggestion:

but if between them all they announced plans that would, over the next 6 months to a year, commit to buying 5M additional shares

My problem with that was that there was a potential to commit to expend more than their respective annual remuneration. In light of this you rightly amend the suggestion,

each person can specify their parameters for purchasing, ie. if the price reaches a certain level, buying is suspended, or if it drops below a certainl level, buying is suspended, or increased, or postponed, etc

Again, I have a problem with this suggestion in that if there is an upper limit, do they not expect the price to rise significantly from there. With the lower level, where has the confidence gone.

I humbly suggest that another alternative would be a monetary value, should a commitment be deemed necessary. Here again, the value will be criticized as being too little, even if the full remuneration package was comitted, I suspect.

Buying, as and when they are able, still apperars the best for all concerned, in my very humble opinion.

Be well