Is it possible to look up information about Steffi Siebner?

She may have been born in Gleiwitz; on 7th September 1897.
She went to school in Breslau,and lived there until 1939.

(Steffi was one of (at least) three children: Stephanie, Kurt and Herbert. Kurt and Herbert served in the Austrian army in the First World War.Can these records be seen?)

They became German nationals in 1918 in Breslau -is there a record of this?

Can anyone confirm Steffi's parents names? - Heinrich Siebner and Natalie Siebner. (We’re not sure her first name was Natalie -it could have been something similar) (Heinrich and Natalie were both 20 years old when they married.)

Natalie had at least three sisters: Lisa Knoche, Clara ? and Paula Angres.Could details of their births be checked?

Thank you.