Well, lucky for you there's an unfriend/unfollow option. You might want to use the block button on the ex though. Just as a precaution.

Stop whining, unfriend them back and block if needed. Problem solved.

And the problem is? Just I friend them, it's that easy.

Delete, block, don't let other people use your Facebook.

just remove them again.

You should probably let your sister know about the friend requests and not to accept them until she gets an ok from you

Dont let your sister use your facebook. Cmon

That's why you always say no and don't just ignore them

Maybe you should talk to your sister about online privacy, so that she knows to be aware of things like this if she ever gets her own Facebook/ social media account.

you have the option to delete the request if you don't want to add them, just for future reference. You can also unfriend and block them if need be.