Here are the pieces I remember. A girl lived in a society with strict rules, parents die and younger brother gets taken into the governing society and doesn't acknowledge sister. The governing body of elites have powers and so does the little brother. I think there is one female leader who is sympathetic to the orphans. The working class lives in trees? and work in a foundry? forging some kind of figurine. They escape into the outer world that the society doesn't believe exists through a deadly fog or mist. I read this I believe 7-8 years ago, not sure if it was a newer book or not but I don't believe it was really old. So I would say maybe 10-15 years ago.
The mystery enshrouding Hutton’s Bridge is as impenetrable as the fog that descended at its borders eighty years ago. Each year, three villagers enter the mist searching for answers. No one ever returns.
Then a dragon falls from the sky to the town square, dead—the first glimpse of an outside world that has become nothing more than a fairy tale to Hutton’s Bridge. Except to Tressa.
Tressa grew up with Granna’s stories of the days before the fog fell. When Granna dies, leaving Tressa without any family, Tressa ventures into the fog herself, vowing to unravel the foul magic holding Hutton’s Bridge captive.
What she discovers beyond the fog endangers the lives of everyone she loves.
Some parts of your description sound like Mistborn by Brandon Sanderson:
The series primarily takes place in a region called the Final Empire on a world called Scadrial, where the sun and sky are red, vegetation is brown, and the ground is constantly being covered under black volcanic ashfalls. Every night the land becomes covered in an unnatural mist or fog.
Some other points that might be similar
The nobility has special abilities
At the beginning of the novel, the reader is introduced to Vin, the main female protagonist