Not a Terraria genius, so sorry if these NPCS can't be obtained this way.
Mostly explained from title, I have four qualified houses, and I defeated Skeletron, and still have not received clothier or dryad. Again, sorry if I'm wrong.
Terraria – I defeated Skeletron and have 4 qualified houses and still have not obtained clotheir
terraria-mobile
Best Answer
According to the wiki, these are the NPCs that will occupy your house a certian event.
Clothier
He is the Old Man guarding the Dungeon. The one that summmons Skeletron when activated. If you have a vacant house, the Clothier will move in.
Dryad
If any bosses are defeated in that world, the Dryad will occupy your house if it is vacant.