Moving out villagers happens when you have 9 or 10 villagers, you can move out a villager 4 days after another villager has left. When you have 8 villagers only villagers can move in until you have 9 then they can move out again. When your villagers are in boxes you can have someone take them and then they won't be voided, you can only get that villager back after cycling through 16 other villagers. You can only have up to 10 villagers.
To get your dreamies, you need to cycle out villagers which like I said above can be done every four days and you can tt to get villagers to move. When you tt four days ahead you will get a ping from a villager, if you don't get a ping it means the villager that wants to move out is at home or in a store so find out who they are by chatting to other villagers. They might say "Oh did you know so-and-so is moving out soon? How could anyone wana leave this place!?" You can continue doing this till all the villagers you don't want have left and your dreamies and come.
Hopefullly that helps!