Teams Meetings and Delegate - Audio Conferencing

Good question! Never tried it. Don't think both need it though (not sure to be honest), so perhaps the delegate as I reckon that info will be attached when the delegate uses the Teams meeting add-in. For not attending the meeting it's a combo of meeting policies set up for the org. (default meeting settings) as it's only the meeting organizer who can enter the meeting options. The "Presenter" role and the lobby setting "People I invite", that is anyone who receives the invitation will join the meeting directly are important to set up (*edited for incorrect wording*).

Now I must test this, too curious how the scenario will look like. Let me know if you get it done before I reply.

Adding a couple of links
https://support.microsoft.com/en-us/office/change-participant-settings-for-a-teams-meeting-53261366-dbd5-45f9-aae9-a70e6354f88e
https://support.microsoft.com/en-us/office/roles-in-a-teams-meeting-c16fa7d0-1666-4dde-8686-0a0bfe16e019