I know how to make a multicam clip for unmodified clips. However, I want to make edits to two clips simultaneously by putting one in the timeline and the other above it like in the attachment (to remove a bad section for example) and then make a multicam clip. Is this possible?
You can't make a multicam clip after it's in the timeline but you can make a compound clip. Before doing that you can cut all layers at once by using SHIFT+CMD+B, move playhead, SHIFT+CMD+B, then lasso to select and delete those.
FCP workflow is designed to first curate all material in the Event Browser -- create multicam clips, mark rejects, favorites and keyword ranges. Then (and only then) start inserting those curated clips on the timeline.
If you later want to add and sync a clip to an existing multicam you can easily do that. Double-click on the multicam to open it, at left of one lane click on the label's down arrow and select "add angle". Drag/drop the new clip from the Event Browser to that lane in the multicam. Then click the desired monitoring angle (the little TV icon at left of each lane). Select the angle you just added, click the label at left and pick "sync selection to monitoring angle". That will sync the newly added clip.
Here are some related tutorials:
Brad & Donna: 8 Ways to Use Compound Clips in Final Cut Pro:
Serge M: Multi-Cam Editing in Final Cut Pro:
Ben Halsall: Use the Range Selection Tool:
Ben Halsall: Fix Layer Gap Problems in Final Cut Pro: