not a problem - setup a call handler with extension 6xxx that handles inbound calls forwarded from that number, create a public distribution list and add the 5 users to it and then set that call handler up to leave messages for the distribution list.
If you're talking about Unity Connection (which I assume you are - 8.5 is not a Unity version) you can also look into dispatch messages with this technique which allows you to have the first person of those 5 that "take" the message then own it (i.e. it's removed from the other user's mailbox when they do that). This is designed for service dispatch like scenarios which may be of interest to you.