Is it important which host/co-host joins the meeting first?
If you added Alternative Hosts when the meeting was created and scheduled, then either the Host (account owner) or an Alternative Host can start a meeting. The first one to join becomes the host. However, it is also possible to give Host permission to another user once the meeting has started.
Remember though - the settings for the person who created the link for the meeting must be set in a certain way for specific tools to be available (e.g., breakout rooms, waiting room, non-verbal communication, etc.). Even if the current host has in their settings that breakout rooms are turned on, if the creator of the link does not have breakout rooms turned on in their settings, this tool will not be available.