I am the son of Regina Davis. In accordance with Arthur's will (so we have been told), Regina, Fred and Jack were placed in care at a local creche for children of impoverished families. She then became fostered to a Swiss couple, but Marie Goldenberg never allowed Regina to be adopted. Regina (her preferred name is Rena) was never told of her biological parents: after WWII her family returned to Switzerland, and Rena's school friends teased her about it. At some stage, Rena broke into the family records and discovered the truth. In 1951, Rena's family migrated to Peru, South America, where she met my father, Colin Dugdale. They had two children in Peru, Arthur Reginald (also known in the family as Reg) and Sarah (known as Sally: she unfortunately passed away in 2007). In 1968 they migrated to Adelaide Australia, and I was born in 1970. Rena has never known much of her family history other than the names of her parents. It was only when we asked to go through her paperwork that we found more details: for example I have a copy of a letter from the British Embassy in Peru stating that Arthur Reginald Davis' father was Robert Edwin Davis, and that he was born in Derby, England, around 1873. Looking into Ancestry.com I can see that there are several records for a Robert E Davis, born 1871, including photos of him in Haifa: the likelihood is that this is Rena's grandfather.
As for Freddie and Jacky, mum's brothers, I know that Jack passed away in 1936 or 1937 of dysentery. We know nothing of Fred, other than he was taken back by Marie and in his early teenage years wrote letters to Rena's foster parents pleading for Rena to be returned to her biological mother.
Rena is still alive, and living in a retirement village in Queensland, Australia.
As you can imagine, it is very exciting discovering more information (and contacts!) for this line of the family tree. I would love for you to reply with any information you have to add to our existing (very limited) knowledge.
I am sorry I cannot provide more information about Marie, but thank you so much for your post, which we found using a Google search! The wonders of the internet!