I could be wrong, but from what I recall/understand:
Chooseyourstory lets authors retain full copyright of their works, so you would want to ask the writers.
The site is given permission to host whatever you put up, but they aren't taking your copyright or whatever.
On the other hand, multiverse infiniverse is funny, since while you might not profit the thing isn't some free endeavour. You say you're a volunteer, how does that work? Who are you volunteering for? Is this a facebook thing?
If this is accurate:
The platform also allows users to place persistent content in the world, which remains in the same physical location even after the user has left the area or quit the application. However, due to the scarcity of real world space, users must purchase or rent land NFTs, which represent the digital layer of real world locations, in order to place persistent content.
And:
Infiniverse has its own economy and marketplace which gives users the opportunity to earn cryptocurrency.
Then it does seem to me like someone could profit from this, or at the very least things aren't as innocent as you make it sound. What happens when someone else buys the 'land NFT' that you put the writers work on? What is infiniverse's outlook on copyright and the content put into it?
If you are just some participant wanting to do what you say, just make your own stories. If I found the correct infiniverse and you are limited by real world space, then being able to ensure the story fits the physical space is a good idea.
But that's just my take.