The Hunt for the Seventh by Christine Morton-Shaw

Jim and his family have moved to a new estate where his father has gotten a new job as groundskeeper in hopes that it helps all of them cope with Jim's mother's death. Jim and his sister have specific areas where they are allowed to go with in the house and if they are caught it means his father will be fired. Jim soon sees that the estate is haunted by six children and it is left to him to find the seventh to avert catastrophe. He makes friends with an autistic boy Einstein. Come to find out Einstein is the 7th ghost and was killed by Lord Minerva. Good suspenseful book but not TU. I'm nay.