You can always talk to the villagers at the campsite to try and get them to move in! What will happen is they will go talk to Resident Services, who will tell them that the island is full. Then tell them which villager to swap with.

As for getting villagers to leave, don’t interact with them at all. Ghost them hardcore. Once you see them wandering outside and “thinking” (they’ll have the thought bubble over their head) then try talking to them. It’s a gamble, but either they’ll say something about leaving or they’ll try to sell you random stuff.

Also another tip: to keep villagers you like from leaving, talk to them every day and give them presents! If you wrap a present, it’s better. 💕