There's nothing scarier than a weird brother or a disturbed sister, and horror movies find ways to make family time even creepier

By Jeff Michael Vice
Special to MSN Movies

Ah, families! Love them or hate them, you're stuck with them. Till death do you part!

Uh, actually, that last part comes from some wedding vows, doesn't it? But, it does seem fitting when you talk about the "Paranormal Activity" movies. These low-budget horror hits follow an ill-fated pair of sisters, Katie (Katie Featherston) and Kristi Rey (Sprague Grayden), who have run afoul of an evil entity.

The first movie scared up some major profits in 2009, due to some imaginative marketing and its "found footage" gimmick. The second film, a 2010 sequel that was also a partial prequel, expanded the story "mythology." And the third, unimaginatively titled movie, "Paranormal Activity 3" (in theaters Friday), also appears to do the same thing, by explaining exactly how the sisters became cursed.

Bing: More on 'Paranormal Activity 3'

If anyone could make this increasingly thin, seemingly limited concept work, it's co-directors Henry Joost and Ariel Schulman. Their hit documentary at 2010's Sundance Film Festival, "Catfish," was unsettling. Correct that, it was pretty darned disturbing.

Evil twins, doppelgängers, conjoined twins and more -- horror films and thrillers are filled with them. Here's our list of some of the more memorable sinister siblings.

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('Paranormal Activity 3'/Paramount)