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.
Luke Jacobz's birth name is Luke Ashwood.
Ned Luke's birth name is Luke, Ned.
Luke Russert's birth name is Luke O. Russert.
Luke Rutledge's birth name is Luke Simon Rutledge.
Luke Shea's birth name is Luke Patrick Shea.
Luke Stambouliah's birth name is Luke Christopher Stambouliah.
Luke Worrall's birth name is Luke J'ean Worrall.
Luke Welland's birth name is Luke Alexander Welland.
Luke Bellingham's birth name is Luke Ian Bellingham.