Who did they marry and when? Do you have copies of the marriage records which should name their parents? Where did they settle in the US?
I did find a marriage in Schuykill County, Pennsylvania for a Ksenia Billa to a Yunko Prebeliak, but no parents are named (civil registration).Her first name is so unusual, that I'm wondering if we're reading it right on the marriage record; perhaps it should be Rosina?
In the 1900 census of Gilberton, Pennsylvania (where the couple were married), I found a few Billey (Billa?) from Austria of the right age to be Ksenia/Rosina's siblings.