Jason Currie dies sometime between the birth of Marvin and the birth of John. Hagar has little contact with her father at this time in her life, and so she does not mention much about her father's death. She does tell us the she got a few pieces of furniture from the Currie home, and that Jason left most of his money to the city of Manawaka. See Chapter 2, P.63 in the M&S paperback edition.
Yes
Gilbert A. Currie died in 1960.
Alex Currie died in 1951.
Donald Currie died in 1909.
Morley Currie died in 1944.
George Currie died in 1978.
Cecil Currie died in 1937.
Raikes Currie died in 1881.
Brainerd Currie died in 1965.
Lauchlin Currie died in 1993.
John Allister Currie died in 1931.
George Alexander Currie died in 1984.