My sister visited me, and now both of my indoor cats are missing.?

You may be thinking "She stole them" but she hates cats and her boyfriend is allergic. It seems like a weird coincidence that they disappeared the same day she came over, though. There are no signs of cat bodies, it's as though they vanished into thin air. I alerted all of my neighbors and NO ONE has any information. Called my local animal shelter so many times that they probably think I'm crazy. On friday it will make a month since they went missing. I've cried so much. One was just a little kitten, only a couple months old :( The other was a large male. I don't know what happened. Is there ANY hope? What could have possibly happened to them?