Query on children of William DIPROSE

Western Australia Death records 540068/1930
William Frederick DIPROSE died 1930 Plantagenet, aged 81, father William DIPROSE, mother Ann NEWALL

New Zealand Death Record 1899/5791
William DIPROSE died age 44

South Australia Birth Records
William Frederick DIPROSE born 6-4-1849 Mount Barker, father William DIPROSE mother Ann NEWALL

South Australia Marriage Records
William Frederick DIPROSE (son of William DIPROSE) married Ann HILL (daughter of Joseph HILL) on 12 March 1878 Daly, South Australia

https://www.findagrave.com/memorial/172104233/william-frederick-dip...

William Frederick DIPROSE 1849-1930 son of William DIPROSE and Ann NEWALL married Ann HILL

https://www.findagrave.com/memorial/164304317/william_diprose

William DIPROSE 1855-1899 son of William DIPROSE and Ann NEWALL married Elizabeth DANIELL

It does seem odd - was one known as Frederick?

Australia, Birth Index, 1788-1922
Name William Diprose
Birth Date 4 Jul. 1855
Birth Place Yankalilla
Registration Place Adelaide, South Australia, Australia
Father William Diprose
Mother Ann Newall
Page number 190
Volume Number 5

Newspaper accounts of the first William have him as William Frederick or W F

Newspaaper accounts of the William who emigrated to New Zealand describe him as the son of William DIPROSE of Melville whereas the other children’s father is described as William DIPROSE of Troubridge.

It still doesn't account for the mother having the same last name? And the nearby siblings being also born in Yankalilla...

Australia, Birth Index, 1788-1922
Name William Diprose
Birth Date 4 Jul. 1855
Birth Place Yankalilla
Registration Place Adelaide, South Australia, Australia
Father William Diprose
Mother Ann Newall
Page number 190
Volume Number 5

I know - its unusual to have 2 children with the same name - but not unheard of.