Buy a Slenderman suit... Ya gotta be dedicated for this one. And every night just stand outside of their windows, or steal some mannequins and several Slenderman suits and put them outside of their houses but hide them during the day. Move the mannequins closer by like a foot every night and play with their cables and switchboards (because that's what slendy does) until eventually the mannequin is close enough for them to notice details, at which point you will have to assume the role of slenderman, and... Well, I don't know what slenderman does when he's close enough to make the kill, or whatever he does. I guess you could just start their houses on fire.