Do these covers work on leather or cloth seats?

These slip over your existing seats. They'll work on both, though cloth seats may grip better during installation. Test-fit before committing to your final position.

Will I need fasteners or adhesive to keep them in place?

Slip-on covers rely on friction and fit to stay put. Most buyers don't need additional hardware, but securing them with seat clips or anchors under the seat frame is an option if you want zero movement.

Can I remove and wash these covers?

Removal and cleaning methods depend on the material and how they're secured. Start with a damp cloth for routine care. Full disassembly for washing is possible but requires patience to reinstall properly.