I found it interesting to read the information in the family site.
I now suspect that the information in the newspaper report which ErikS cited was wrong. I could perhaps envisage one person escaping from custody after being arrested by the Nazis - but two? Obviously Moritz Ostier, his father, mother and other family members were able to leave Austria. And, unless some one outside Austria paid their way, they took some assets with them.
The information in the family tree gave me one other idea about the family's location in Vienna. Could that have been a residential address -- that is could the family have rented an apartment on one of the upper floors of the building? I note that a phone number was given so the information may have been taken from an old telephone directory.
Another aspect to the firm's history is whether Marianne Ostier designed the jewels for Queen Geraldine of Albania.