How to film a Video with the whole frame in focus, not just certain focus point(s)?

Hey everyone! I'm new to photography and my Nikon D3100. I'm going to have to film a talent show for my club (I'm the historian of that club), and I need tips on how to effectively film the performances.

My camera can film up to 10 minutes, and I'm just using the lens that came with the camera without any other lens. How do you make the camera focus on the whole frame, not just certain focus point. I want to make the whole view clear, as my group will be participating in the talent show as well and I'm not able to focus it during the filming. We will be dancing (there are 3 of us) how do you focus on all 3 of us at the same time.

Also, when I film other people, how do I focus on them without the camera going out of focus and focusing again. I've done some tests but I just can't get this figure out.

Better, I just want the whole view to be in focus the whole time

Thanks

I think it would be best to switch to Manual focus (there's a switch on the lens) and focus yourself especially if it's a talent show where there will be a lot of movement. The autofocus trying to focus by itself will also be very noisy and might be heard when you play the video back.

I'm in the same boat... But it's so hard to do manual focus when you can't even look through the viewfinder. The display screen can be so difficult to see detail in, how can one use manual focus to film with it??

oh. my. god. thank you.