What would servants in noble house call each other?

It would be very unusual for any servant to address his or her superior in age or rank by first name.

In general, the English usage of the time was that among the servants, the housekeeper and female cook would be called "Mrs. Lastname", the butler would be called "Mr. Lastname", the valets, footmen, and senior outdoors staff (head gardener, head groom) would be called "Lastname", the ladies' maids would be called "Lastname", the nannies and nurses would be called "Nurse Lastname" and "Nanny Lastname", and the housemaids, kitchenmaids, and junior outdoors staff would be called by their first names.

The only difference between abovestairs and belowstairs usage is that the employers of a butler call him "Lastname", while his colleagues call him "Mr. Lastname". Thus:

"Mrs. Hudson, can you tell me whether Jeeves has gone out?"
"Mr. Jeeves left about an hour ago, sir."

A male cook in a 19th-century English household was generally French (or pretended to be); he would be called "Monsieur Firstname" or "Chef Firstname" by his colleagues, and "Firstname" by his employers.

People in service generally preserved formalities of address among their peers; two footmen having a conversation would call each other "Smith" and "Jones", rather than "Tom" and "Bill" unless they had been childhood friends (and even then, they'd probably fall in the habit of more formal address).


As for the German usage, can't help you there. However, there's an added element to German conventions of formality/informality, as there are formal and informal second-person pronouns. It would be odd for a housemaid to address a butler as "du" rather than "Sie".