Goblin Island by Elsie J. Oxenham

The Colquhoun family suffered a great loss when Mrs. Colquhoun died. Peggy, who was eighteen at the time, and the eldest daughter, returned from boarding school to play the role of mother. Shortly afterwards their father also died and they were left in a very serious financial position.

To economise was absolutely necessary; but how were they to do it? It was decided that they should live in a cottage on a small island which luckily was their own property.