This has worked for me, maybe it might work for you.
Make a new character and talk to everybody ONCE. Then talk to everybody you want to keep as you would normally. Do not play as your main character during this process. While playing as this new character, ignore only the villager you want to leave. After a few days to a week, they'll most likely want to move out. If you need clarification, the youtuber pwanapplz (I don't know if thats the rxact name) does a great job explaining it.