These are the books by Alan Temperley that are reviewed on this site:
Suddenly orphaned, rich little Harry shrugs off his horrible nanny and goes to have larks with his old aunties. But his aunties have quite a hobby . . .
Eerie tale of evil enchantments in a Scottish glen.
Life is not easy for Silas the ragboy. But his luck changes when he meets a distressed mermaid on the beach after a storm and decides to protect her.