By host, I assume you mean Organizer. That is the GoTo term for the person who hosts the webinar.
I often have two or more Organizers in a single webinar. I am usually pushing the buttons and generally ensuring the technology works. I usually have another Organizer who keeps up with the Questions that the Attendees submit and pass the relevant ones to the Presenters. Sometimes I have another Organizer who is just the time keeper and interrupts Presenters who go past their allotted time.
Extra Organizers can join the webinar using the same user name and account password that you use to start a webinar. If you don't want to share the password (very wise), you can promote someone during a webinar to be an Organizer. (That's how I do it.) Doing that will give that new Organizer all the rights you have as the main Organizer. We usually call these folks Co-Organizers.
It is expected to have all of the Organizers and Co-Organizers on separate computers. If for some reason these people are on separate computers in the same physical room, then you will have to deal with microphone/speaker/echo/feedback issues, which is the topic of a different discussion.
Your Co-Organizers can do anything you can do within the webinar. It would be best to host a test webinar to let the new Co-Organizers get a feel for what they can do during the webinar and things they should not do. Training for new Organizers is important. You don't want one of your Co-Organizers accidentally ending the webinar for everyone just because they have to go to another meeting. Co-Organizers can also accidentally kick someone out of the webinar when they are just trying to un-mute the Attendee.
One thing to be aware of is that there is a limit of 25 total Organizers and Panelists at one time during a webinar. If you have only one or two Presenters, this is not a problem. If you have a day-long webinar with lots of Presenters, then you might reach the maximum and have to rethink the number of Organizers you will have in a single webinar. This would be a rare occurrence, but I have maxed out on a few occasions.
Once you have promoted someone to be an Organizer or Panelist within a webinar, you can not take that privilege away from them. After you make someone an Organizer, the only way to make them a regular Attendee is to kick them out of the webinar and let them rejoin the webinar.
