What comes in the split king set?

Four pieces: two twin XL fitted sheets, one split king flat sheet and two king pillowcases. That covers both halves of an adjustable split king base.

Will the fitted sheets fit a split adjustable base?

Yes. Each fitted sheet is sized for a twin XL mattress, which is what split king bases use. Check your mattress depth, since thick toppers can make the pockets tight.

Is 400 thread count Egyptian cotton good?

400 is a solid mid-range count for sateen: dense enough to feel smooth without the heaviness of very high counts. Some very high thread counts are inflated by multi-ply yarns, so this figure is realistic.

How does sateen differ from percale?

Sateen has a smoother, slightly shiny surface and drapes more softly. Percale is crisper and more matte. Sateen suits sleepers who want a silky feel; percale suits those who want a cool, crisp sheet.

How should I wash these sheets?

Machine wash warm with like colors and tumble dry low. Skip fabric softener, which coats cotton fibers, and avoid high heat to limit shrinkage and wrinkling.

Yes, cotton sateen wrinkles, especially if line dried. Tumble drying on low and folding promptly reduces creasing, but some wrinkles are normal for cotton.