If you think your Instagram Lives have been getting a bit lonely and dull, the app will now let you add a friend to join your live stream. The catch is your friend has to be watching your Live Story to join in. So make sure to let that person know you want them to live stream with you ahead of time. It’s pretty simple to setup. You just need to tap on the two smiley faces seen at the bottom of the screen (beside the comments text box). From there, your screen will be split horizontally and you just need to select the username of the person you want to stream with. If you want to take them out of the stream, you just need to tap on the X button on their screen. Just like a regular Live Story, you can add filters and the like as well as opt to not make the video available for 24 hours.
Source: CNET