The Dream Travellers — Sherry Ashworth

When a mysterious lodger called Dolf Hunter comes to live with 12-year-old Sam Kenyon and his family, it's the beginning of a seriously spooky adventure. For Sam has seen the man before—in a nightmare. His friends decide to trail him and learn that Dolf makes straw-dolls that will allow them to visit each other's dreams. Each child has a separate dream kingdom; Sam's is a forest, Amy's a moonscape, while Dean's is in the mountains and Hannah's is centered on a most unusual city. At first, the children have fun visiting each other at night in their imaginary kingdoms, but soon they become increasingly aware that someone—or something—is stalking them in their dreams.