When you turn off video chat, cameras and microphones are disabled for everyone in your room.
At the bottom of your screen, select your room name, hover over Room Settings, then Disable A/V for All in order to prevent anyone in your room from turning on their mics/cameras. After disabling A/V, you'll see a pop-up confirming this is done at the top of your screen.
At this time, it's not possible to disable cameras and microphones separately (room owners can on iOS). We'll be expanding these features soon.
Mobile (Android, iOS)
At this time, it's not possible to disable A/V on mobile. We're currently working to restore this feature.