If your guests aren't there as part of a Stayover, you can get rid of them by traveling.
Have one of your active sims set up traveling with the unwanted guests to another lot, preferably in a different town.
Once your sim arrives there with them, your sim can simply go home and abandon your unwanted guests there.
I typically lock my sim's front door to "Lock for Everybody but Household Members."
Non-household sims can access the front yard, but they can't get into the house4.
In my current save, my sim has an extra club that consists of himself, his parents and grandparents.
He never gathers this club but he uses it as follows:
*Set front gate to "Lock for everybody but household members"
*But "Allow access to..." the club with my sims parents and grandparents.
Good luck! Uninvited "guests" are such a pain!