To do a split screen you put video #1 on track one. Put the next video on a higher track and use a mask to allow video 1 to show through how you want. Same with video #3.
To make the video stop you can use a freeze frame or screen shot. Set the slider at the point where you want it to stop. Right click and choose Edit Video/Image then Freeze Frame. You can set the image duration as long as needed.
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