All of them, im fairly certain. All new villager will probably arrive without houses and need to build them, including the original two. This would allow you to choose their placement.
Agreeing with the others here - it just wouldn’t make much sense to limit it to the starting villagers.
I think they actually made an extremely clever move by having the Animals start out in tents as well, since tents are in fact easily moveable and mostly temporary in real life.
That way we can get a feature we’ve been hoping for without it seeming too unnatural (like picking up and relocating a solid structure would be!)