I look forward to what is posted here. My mother was born in Semun, in 1943. German.
I’ll see if I have any information.
I did however just do a brief search for you on Familysearch.org, there are a lot of Sarics, from Belgrade Yugoslavia back to early 1900’s so maybe check that? https://www.familysearch.org/search/all-collections/results/?q.surname=saric&q.birthLikeDate.from=1900&q.anyPlace=Zemun
I read that Zemun was a separate town that was absorbed into Belgrade in 1934.
Also, there are some great DNA tests, my husband did the “Big Y” haplogroup, which follows the fathers side. Perhaps that might help? Not sure though how much information you get for your husband's mother’s side.
I found that my heritage it seems to have more European genealogy than Ancestry. But maybe Ancestry is catching up now. I was also contemplating hiring a researcher, as I did for my dads family. He was born in East Germany/ East Prussia. They were immensely helpful.
Incidentally, for my husbands side in Scotland, we found great information on wiki tree- and you can connect to this one world tree with various DNA tests. It’s pretty amazing. (Not much for Yugoslavia/ Germany though, at least not yet but you can start your tree and a search)
Best wishes
and Happy New Year
Anita Stonawski- Semple