voluntas , in order to facilitate cooperation for the game development, first you should setup an appropriate infrastructure to make that happen.
In more technical terms, you will need to share the game (not the images, animated or static) code, which is basically the HTML file with embedded Sugar Cube framework code and probably CSS too.
The best way to share code is to have it stored in a Concurrent Version System. There many options for that, but Git is the most used one, by far.
I did some research and we can work with the game HTML file (which size is about 4MB) without issues (but it would be much easier if the game is built with multiples smaller files, like with the Twee framework works).
It's important to have it for a very simple reason: I saw that you're working in a new release (after I made changes to the previous version), and all the improvements that I made you need to be "moved" to this new code base. That's a hard thing to coordinate manually, Git would definitely help managing that. And there a lot more interesting features, like being able to revert changes easily.
So, for starters, you need to go and take a look to services like Github and Gitlab, which are free services. An important caveat is that you will need to check if you can have the game code over there due any policies the services might have, after all, that's content for an adult game.
And last, but not least, you will need to decide if you want the code to be freely available by creating a public repository or setting up a private one, which would give a better control of who might want to have access to the code.
Given the fact that the code runs in a browser, it is relative easy to get your hands in the code if you have basic knowledge of HTML and Javascript, so from a technical point of view, there is no much sense in having it in a private repository. Choosing an appropriate software license (GPL3, Creative Commons, etc) that is aligned with your objectives for the game is also important.
This is a very important step, so take you time.
If you prefer to keep things simple by now, I can try to create patches (technical term for injecting code changes) for the current game and provide them here, with instructions on how to apply those patches to the HTML file. Just let me know how do you prefer to do it.
