I have no experience here but could you add weight to the others to make them heavier? Maybe tape strips that will have minimal aerodynamic impact? If not, maybe sand or shave down the heavier ones until they match?
Physics
I don't believe that the reason for this is density changes of the wood but more likely imprecise dimensions.
I can't really tell from the picture, but the lower blade seems slightly larger or maybe even thicker.
For example, the section marked in green at the heavy blade seems to be bigger than the blue marked section of the light blade. So I would suggest sand paper.
Could be. I'll try a mix of grinding and hollowing probably.
Drill a hole in the heaviest one then use putty to cover the hole back up. For the one that's just slightly heavier you could probably remove enough with sandpaper to even them out.
Sounds relativly easy and functionable, I'll try it in this way probably.
Make the heaviest hollow?
Yeah, or cut a hole in the blade and fill it up with something lighter. I'll try it in this way probably.
Can you drill from the faces closest to the center of rotation on the heavy ones?