sadly, there's no way to change or avoid adopting your 1st campsite villager; you're stuck with who you get
as for evicting villagers, there's no foolproof way of doing so as the game doesn't give us an option to do so. the best way to move someone out is by time-traveling (
here's a compilation of guides showing multiple ways how); if you don't want to time travel, the best you can do is not speak to them after you've introduced yourself, and then wait until they wanna leave