Do these mount directly to factory holes?

Yes. These bolt at the factory mounting points — no drilling, no custom brackets. Just remove the old markers and bolt these in.

Will I need to wire these differently than stock markers?

LED markers draw less current than incandescent, so they'll work on your existing harness without modification. Your electrical system will thank you.

What happens if one bulb burns out?

LED units are sealed assemblies — if a bulb fails, you'll need to replace the entire marker light, not just the bulb. These come brand new, so failure out of the box is extremely rare.