Edith Twiasschor's birthdate is given on a British security document

Edith Twiasschor was born in Berlin on December 20, 1911, a very proper 11 months after her parents married in London.

I have not yet found her actual birth record, the information comes on this British security document from November 1939, when she was 28 years old and already resettled in England. It provides her with an exemption from internment as an enemy alien. Although she is a German national, she has refugee status and is therefore exempt. 

Edith's birth date in 1911 makes her almost 13 years older than Helga. I'm still looking for any record of Gina; this would suggest that she is the younger sister.