The Professor DID have a servant then... Mrs. MacReady. She likely cooked as well.

For a single owner of such a large house, the Professor probably kept most of it shut up and unheated, living in only a small set of rooms. The unused rooms could have opened p for tours and the like.

@cobalt-jade He also had the maids, Ivy, Margaret and Betty.

@narnian78 it was traditional in larger houses to call senior female domestic staff 'Mrs', whether or not they were married. It was an honorific relating to their position as housekeeper or cook. In the1930s, plenty of English women were unmarried, as so many young men died in the Great War. 

Between the wars there were far fewer people working as domestic servants, as working class people had more opportunities. By WW2 this house had only three maids and the housekeeper, and we assume any male staff had enlisted by the beginning of LWW. 

The Professor's owning the house was nothing to do with his income, merely inheritance. 

Evacuating children from London required all people in rural areas to offer accommodation if at all possible. The Pevensies were fortunate to be in a country house with gardens to grow food that was otherwise rationed. If there were hens, they could have more than the one egg a week per person.