Will these yellow or turn hazy in the sun?

Carbon fiber is much more UV-stable than clear-coated plastic. That said, these ship with a protective clear coat finish. Keep them clean and avoid prolonged direct sunlight storage, and they'll hold their gloss for years.

Do I need to seal the edges where the visor meets the window frame?

Not required. These are designed to sit flush against the factory mounting points and handle normal moisture exposure. If water pooling becomes an issue during heavy rain, a small bead of clear silicone along the bottom edge will handle it without damaging the carbon finish.

How much harder is installation compared to plastic visors?

Carbon fiber weighs less, so there's actually no added difficulty. Mount them the same way you would any window visor — align with factory points, secure with included hardware, and you're done in about 20 minutes per side.