Each Team is also a group, so you can invite the group name. This will put the meeting in the Groups calendar, and will also be sent to each of the groups members (by default, they can opt out of receiving).
I'd just send out a Meeting invite, Send a link to the channel (Right click channel get link). Then say go the channel and join meeting. You get on a few minutes early, start an adhoc meeting in the channel and boom, there ya go. If your trying to make it private then your meeting invite method is the way to do it using the Teams button. Otherwise you can do a Group chat ahead of time, then start a meeting in that group chat.