Ask HN: How to pay devs evenly on product?

Hi I am making a new agency for developing a portfolio of niche saas products. My ideal is to split all profits accordingly:

50% goes to buying (read: freeing) up forrest land.

50% is split between all devs on the individual products.

My questions are (and here only regarding the 50% not going to forrests)

1. How to split the profit amongst devs in a fair way?

1.a. Should it reflect their level of contribution?

1.a. Should it be for life? Contribute once, get paid forever

2. Do anybody know if this sort of scheme is applied elsewhere?

My goal is to make products that contribute to wellbeing both in environment and on the human level with open transparent products. Goal is not initially to create a living foundation for anyone but instead to create a secondary pay (i'm interested in keeping my dayjob :-)

All code is aimed at being opensource