José Ygnacio Castro had an older brother by the same name who died in 1811. As a young couple living with his father, Ygnacio Castro and Ricarda Rodríguez, my great, great grandparents, had four children who survived to adulthood.

Per mission records:
José Ramón de Jesús, baptized at two days old, May 18, 1838 SCZ# 2305
José Simón de la Trinidad, baptized October 28, 1839 SCZ# 2325
Maria Ygnacia del Espíritu Santo Castro, born February 1, 1845, baptized February 16 SCZ# 2728
José Ignacio Mauricio, born September 22, 1847, baptized May 19, 1848 SCZ# 2798

In his 1858 will as documented by Leon Rowland, he states that his children are "José Ramón, José Simón, José Ignacio and Maria Ignacia".

Per LDS records:
José Ramon Castro 1837–Deceased
David Castro 1839–1905 appears to be the same as José Simon Castro 1839–1906; married Antonia Amada Vasquez, November 28, 1877 in Monterey and had 4 sons and 5 daughters.
Maria Ygnacia Magdalena Castro 1840–1896 See her link below for corrected information. The 1841 census lists "Josefa Mojica", but not in the 1843 census, so Josefa might be a deceased daughter born in 1841.
It appears here that twins, a son and a daughter born in 1844, did not survive:
Maria Castro 1844–Deceased: this might be the surviving Maria Ygnacia.
José Castro 1844–Deceased

Residents of the Rancho San Andrés Castro Adobe:
It appears that the young couple had their own adobe on the premises, with an elderly relative, in the 1836 census for Villa de Branciforte (CAMD)
Rancho San Andrés:
Household #1 Joaquín Castro, 67, Maria Rosario Briones, 20
Guadalupe Castro, 22
Joaquín Castro, 15
Juan Bautista, 02
Ygnacia de los Angeles, 04

Household Number #2 Juan José Castro, 29, Maria Rita Pinto, 33
Manuel, 10
Guadalupe, 08
Trinidad, 06
Jesús, 04

Household Number #3 Ygnacio [Castro], 20, Maria Ricarda Rodríguez, 18
Maria Manuela Tapia, 68 {She was Rita Pinto's mother, widowed 10+ years.}

1852 California census, Santa Cruz:
Ignatio, 32 farmer
Ricarda. 28
Ramon, 14
[male] 12