PIP = one video per placement.
1. Place the video into PIP
2. produce your video
3/ Bring the produced video back into the Time-line
4. Put your second PiP into the PiP time-line and position
5. Produce the video for a second time
You will now have two PiP displaying in the same place if you did the editing bit to align etc.
Repeat the procedure for PIP's 3 and 4. Then do a final Produce and have 4 PiP's displaying at the same time...easy peasy.
Dafydd