If people join together for a commercial product, they need to do so formally. Any product that intends to sell commercially better use a single entitiy that enters contracts with the publisher and the publishing platforms. And anything with a promise of revenue share is bound to be a commercial thing eventually. Even if only pocket money trickles in, or is expected.
Joint copyright is a pain. And unregulated, this is what would happen to the project. So each participant could sell the product any way they liked - under obligation to share profits with the joint copyright owners. Try enforcing that, if the people are all around the world. And how would platforms react, when multiple people tried to sell the same product. Which they legally could try, under joint copyright.
For Itch, this section of the tos is interesting:
Publishers affirm, represent, and warrant that they own or have the rights, licenses, permissions and consents necessary to publish, duplicate, and distribute the submitted content.
Joint copyright does not need consent. In my opinion, it is a royal pain the nether regions.
Which is where your project wants to fill the gap. Provide structure, contract templates, remind people to actually enter a contract before committing months of work and so on. And of course, help in other ways.