Were they from Texas? If so, there is a Gertie M Jackson that died in Oakland in 1990 and Herman D. Jackson that died in Oakland in 2001. You will notice that both of their SSN's were issued in Texas.

Name: Gertie M. Jackson
SSN: 465-XX-XXXX
Last Residence: 94609 Oakland, Alameda, California, United States of America
Born: 19 Dec 1914
Died: 12 Jan 1990
State (Year) SSN issued: Texas (Before 1951)

Name: Herman D. Jackson
SSN: 455-XX-XXXX
Last Residence: 94605 Oakland, Alameda, California, United States of America
Born: 11 Dec 1925
Died: 14 Jun 2001
State (Year) SSN issued: Texas (Before 1951)

If that is them, then you maybe to find them in the Census.