You can absolutely have multiple names in a copyright notice, if the licensed work has multiple authors. In some jurisdictions there's also the concept of “joint authorship” that might apply here. You hold copyright automatically by authoring something. It is unnecessary (and quite unusual) to create a legal entity to hold the copyright.
Some projects with many contributors do not list everyone in the copyright notice. Instead, they might only list the project founders, or may just say something like “the project contributors”. This isn't a problem because copyright notices aren't terribly important. They aren't a complete list of authors, but more of a reminder that someone holds the copyright for the licensed work.