well im not sure if your friends can make your villagers move out or not, but my brother did the same to me... he visited my town and talked to Becky (the chicken) a lot and then she decided to move out... but before she did that she asked me what i thought and i told her to move (since i wanted new neighbors). but as whether or not my bro had anything to do with it, i'm not sure.
Don't worry, they ask you a few time and if you like them, you can tell them "don't move" and if you want them to move you can tell them to "please move".
so you can still convince them to stay if you like them. just keep telling them to not move everytime they ask you, and most of the time it will work.
but if they do move, within a few days you'll get new neighbors... no worries!