CUC wasn't designed for group mailbox functionality for concurrent access. It has been done before though. The same concept exists with Microsoft O365 as with Gmail. Just remember that CUC delivers to a single email address. You could have an individual mailbox in CUC that has a unified messaging email address such as group1@company.com, it'll send the voice messages there. In O365 you'd have a group mailbox configured with group1@company.com as its email address and the members would all have access to that mailbox. Same concept for Gmail, looks like this document explains how groups can be created and assigned an email address: https://support.google.com/a/answer/9400082?hl=en#zippy=%2Cstep-create-a-group
Another way this has been done is a distribution list is configured in CUC and you'd assign all of the necessary users as members of that DL in CUC. When a message gets addressed to that distribution list, CUC will send that voicemail to all of users individually, who belong to that DL. This would require you have a call flow in place (Call Handlers, routing rules, etc.) that route callers to this distribution list.
