Will these visors yellow or fade in the sun?

Carbon fiber style panels can yellow over time with UV exposure. A UV-protective clear coat applied after install will slow this significantly. If you're in a high-sun climate, plan for a clear coat layer during installation.

Do I need to seal the edges where the visors meet the window trim?

Edges are not sealed at the factory. You can run a small bead of clear silicone along the top seam if you want extra weather protection, but it's optional for most climates.

What's the best way to clean these without scratching the finish?

Soft microfiber cloth and mild soap water work fine. Avoid abrasive cleaners or rough towels — the carbon fiber finish scratches easier than painted trim.