List collaboration (multiple members editing the same list) is not supported at this time.
Some lists on the Official Lists account mention a list maintainer in addition to the list owner—this feature is available to crew-maintained lists only, so that we can give credit to the creators of important lists such as our Top 500 of all-time.
While collaboration is not officially possible with our current tools, one way of compiling a list from multiple sources is to use our Import tool, which accepts list CSVs output via the Settings → Data tab on our website. Using this approach, a member could import contributions from other members (as CSV exports) and publish the combined list, with the caveat that there would be no automated way to remove a film from the list using this method.