Hi Palace,
How sure are you about the dates of birth of Joseph Spillane and Mary Twomey?
The marriage of Mary Twomey and Joseph Spillane in 1940 records:
Date:11th June 1940
Groom: Joseph Spillane, Bachelor, Full age, occ: Victualler, abode: 38 Parnell Place
Bride: Mary Twomey, Spinster, Minor, no occ, abode: Endsliegh Park
Grooms father: Peter Spillane, occ: Victualler
Brides father: John Twomey occ: Insurance Supervisor
You give Mary Spillane's (nee Twomey) birth date as 23rd Jan 1910 but she is recorded in 1940 as a minor (under 21) also her death in 1979 records her as being born in 1920.
If you look at the 1911 census link that I posted above you will see that Peter and Elizabeth Spillane are living at 38.2 Parnell Place and that Peter is recorded as a Victualler.
Peter Spillane married Elizabeth Crotty on 14th Oct 1902 at St Peter and St Paul Cork
Groom: Peter Spillane, Bachelor, full age, Occ: Victualler, abode: 2 Parnell Place
Bride: Elizabeth Crotty, Spinster, full age, occ: Dressmaker, abode 8 Wandesford Street
Grooms father Peter Spillane occ: Victualler
Brides father: John Crotty occ: Painter
Peter is recorded living with his mum and dad Peter and Mary Spillane in the 1901 census at 2 Parnell Place (see 1901 census link I posted above)
If you look at all the above info it looks very much like the birth reg that I posted above is your great grandfather Joseph. (The only thing that does not fit is the date of birth that you give for Joseph Spillane)
The link to the birth reg that I posted for Joseph Spillane records:
Born Date: 21st May 1911 Place 38 Parnell Place Cork
Name Joseph Mary Augustine Spillane
Father: Peter Spillane of 38 Parnell Place occ: Victualler
Mother: Elizabeth Spillane (formerly Crotty)
(Joseph's father Peter registered the birth on 9th August 1911)
Chris