Family legends should be taken with a grain of salt. They can sometimes be completely accurate or completely wrong (or only partially true). How sure are you of his parents' names? Are they listed on his Social Security application? Was he Roman Catholic? He may not have talked about his parents much because he either didn't know much about them if he was orphaned as a child or it was a painful subject.
I'm assuming you are referring to the John Jacob Walker who died Jan 28, 1981 in Florida. If so he was born Sept 16, 1892 according to Florida death records, however his WWI draft card shows he was born Sept 16, 1894 in Marion, PA. He was allegedly married to Eva Hampele in Reading PA in 1918.
Some researchers have his parents as Hugh and Lena Walker based on the 1900 census of Allegheny County, PA. If this is him then he had 3 siblings Robert A. 1897, Marie G. 1900 and Hugh W. 1902 (who died in Illinois in 1936 - see familysearch.org).
A 1906 death certificate for a Hugh Walker 38 shows he died in from injuries sustained in a fight.A John Walker 15 is listed as a ward of St Joseph Protectary for Homeless Boys in Pittsburgh in the 1910 census. Coincidentally, a Robert, Marie and Hugh Walker are listed as inmates of St Paul's R.C. Orphan Asylum in Pittsburgh with ages that match fairly well with the 1900 census and Hugh's death certificate.
The 1920 census lists a Robert, Marie and Hugh Walker living in Cambria County as the step children of Jesse Murphy (again the ages match well). Jesse's wife is listed as Marie L. 42.
A PA death certificate for Marie L. Murphy shows she was born May 17, 1878 in County Cork, Ireland and died Feb 4, 1937 in Johnstown, PA. Her maiden name is listed as Hayes. Coincidentally on familysearch.org you can find the 1895 marriage record of Hugh Walker and Lena Hayes. He was born Sept 17, 1868 in Ireland and she on May 17, 1873. Yes, I know 1895 is after John was born.
All nice coincidences but so far that is all they are. I suggest starting by getting your John Walker's marriage record. If he did marry Eva then the Berks County Orphans Court should have the record. Be sure to ask for the application which will have more information. If you feel I'm on the right track check with the Archdiocese of Pittsburgh to see if they can help you find information on when he and his siblings were put in orphanages. You could also try to track down Robert, Marie and Hugh's obituaries. Presumably they may list John as a surviving sibling. If Marie was his mother than her obit should list John as a surviving son.
However, if you feel you have the correct parents and I'm wrong then knowing something about other members of his family may be helpful. For instance knowing the name of the aunt could be very helpful.