well... their sisters name is rebecca st.james...
The last name of Luke or Lucas originates from several different European countries: it can't be situated without knowing a bit more about your family history. In addition, "Luke" is a spelling of a common Cantonese name and/or Vietnamese name--so it could come from there, too.
Luke Rutherford's birth name is Luke White.
Ned Luke's birth name is Luke, Ned.
Luke Jacobz's birth name is Luke Ashwood.
Luke Russert's birth name is Luke O. Russert.
Luke Rutledge's birth name is Luke Simon Rutledge.
Luke Bellingham's birth name is Luke Ian Bellingham.
Luke Benward's birth name is Luke Aaron Benward.
Luke Pierce's birth name is Luke Russell Pierce.
Luke Shea's birth name is Luke Patrick Shea.
Luke Stambouliah's birth name is Luke Christopher Stambouliah.