I'm looking for two books which I read in 2000 or 2001. The plot of the first was about two or three children that were looked after by a nanny with an umbrella. Near the start of the book they find her dead in an armchair next to a cup of tea and they think they've killed her. I think they hide her somehow, but then she keeps popping up and they can't get rid of her. At the end of the book, their house is burnt to the ground and their parents are driving them away. The parents tell the children that the only thing saved from the house wreckage was an umbrella, and they turn to see the nanny sitting behind them in the car.

The second I think was part of a trilogy. It was about a family with two sisters that moved to a house. The house was haunted and one of the sisters ends up dying in the walls of the house. She becomes a ghost and haunts the other sister and tries to ruin her life. At one point she pours something all over her, and I think the alive sister sees the ghost at one point and tries to talk to her.