Repositioning the Vertical video on iMovie

Yes, you can display your vertical video on the left side of the screen.

Place a black background in the time line and drag its edge to adjust its display time as much as you need. Then place your vertical video in the upper timeline above the black background. Select the vertical clip in the upper timeline. Click on the overlay icon (the one that looks like overlapping squares) in the toolbar at the upper right of your screen. Select Picture in Picture from the selection box. Adjust the size and position of your vertical clip as it appears on the preview screen. Move it over to the left side. Then click the blue reset button to the right to apply your changes.

After you have adjusted the first clip to the left side, you can add your other vertical clips above the black background. Then select the first overlay clip that you already adjusted and do an Edit/Copy. Select all of the other clips as a batch and do an Edit/jPaste Adjustments/Video Overlay Settings. That will paste the exact left side clip position that you used for the first clip into all of the other clips.

-- Rich