Children's book about WW2, published late 60's to early 1970's

I'm trying to find the title and author of a children's book read to me in the 1970's. The protagonists were two young sisters, at least one preteen, the other a little older, and the story is the older girls point of view. They are in Leningrad during the 500 day siege in WW2. Food can only be delivered to the city by trucks driving over the frozen water and I think their older brother (or uncle?) died when his truck broke through the ice. In an early scene the father gives each girl a necklace, expensive real gems because he knows the Germans will assume anything a child wears would be fake. The daughter talks about he has a sparkle in his eyes and often gives random gifts not bothering to wrap them.
The girls leave the city alone and the younger of the two tries to sell her gem but the jeweler first things he is playing along with a child, then realizes it is real and tells her it is too valuable for him to buy. I think he gives them some food or money but lets them keep the gems.

This would be been read to me in 1974 or so.
Thank you in advance!
Tim

In Journey to America by Sonia Levitin the sisters are each given a ring by their father, and later in the book a jeweler refused to buy them. I don't think other details match up though.

It is possible I'm confusing details from two books, Mom read us "Boris" by Jaap ter Haar, so the food scarcity and such may be from that book instead. Looking up Journey to America, I'm not sure the release date. Amazon says it was published in 1987, so too recent, but if it was published in the 1970's then it is probably the correct book.

I think the original publication date was 1970!

It's c1970. Worldcat.org is more reliable for the least recent date (list sort).