To address the original question, rights holders can give the rights to their properties to whomever they want, and derivative rights are all separate from each other - so a right holder can give film rights to one party and stage production rights to another, for example. The key is what the contract between the rights holder and the derivative author details. My guess is that Amazon bought the exclusive rights to any film adaptations, and that would bar another party from doing the same.
That’s a very general overview but considering that this Amazon, I’m sure that a) a team a lawyers pored over the agreements and b) plenty of money was spent to make sure that all rights were exclusive and as broad as possible.
There has been talk about some other project dealing with other Ages and that’s possible because it is outside the rights granted to Amazon but if you’re looking for a third party to step in to my would either be buying the rights from Amazon or it would be far in the future where Amazon’s rights terminated.