Keeping sound from underlay video in creating PIP video with ffmpeg
Ah I found the answer to my question, I ventured into the ffmpeg documentations again and found that all I had to do was add -map 1:a in front of output.mp4 and I also added -c:a copy cause I thought that copies the same codec settings from the original videos or something, not really sure but it seemed better then putting all those specifications in like I did which I actually just left in there from the site that I found the main part of this ffmpeg command on.

My code is now working as I want it and I'll share it below:

ffmpeg.exe -itsoffset 35 -i overlay.mp4 -i underlay.mp4 -filter_complex 
"[0]scale=700:-1 [overlay]; [1][overlay] 
overlay=main_w-overlay_w-30:30:enable='between(t,35,552)'" 
-map 1:a -c:a copy output.mp4

The itsoffset is the time before the overlay video starts playing, between(t,35,552) means the overlay video is visible between the 35th second and the 552nd second on the timeline of the output video.