Video overlaying, 1 video in another video

Question

Hi, i need help with video overlay in Visual studio C# to create an overlay video, the following is my needs.

1) able to embed/overlay one video into another video, at a corner of the other video(best if can select position)

2) videos sound are not affected

3) able to render both video into 1 single video with the overlaying effect

I had tried to look up on information on overlaying but there wasnt one that taught me how to do all these, i really need help now so i would appreciate if anyone could help me thx