Do you know if the half siblings were older or younger?
There's this family in the 1870 census for Louisville, Clay Co, IL: MCBRIDE, John age 23 b. KY Mary age 22 b. IN George W. age 1 b. IL
What is your source for George's father being born in Ireland?
The 1880 census for the same location has an 11 yr old George MCBRIDE listed as "other" in the household of A.F. & Margaret DETWEILER.In this census it states both of George's parents were born in IN.
I see in both 1910 and 1920 where he is in Macoupin Co, IL that he states his father was born in Ireland.In one census he says his mother was born in IN and in the other he says Germany.
There's this family in the 1900 census for Louisville, Clay Co, IL: LAMBKIN, Alphonso b. Aug 1873 in IN, married 5 yrs, father b. IN, mother b. KY wife Mary b. b. Aug 1845 in IN, 3 children born, 3 children living, father b. IL, mother b. IN stepson LAMBKIN, James b. May 1883 stepson LAMBKIN, John b. Feb 1887 stepdau LAMBKIN, Cora b. Jan 1888 father-in-law MCBRIDE, George b. July 1832
If it's the same family, the ages for Alphonso and George don't make much sense.I'm guessing that George's age, 32, was mistakenly recorded as his birth year.I don't know why it says father-in-law instead of stepson.
I found Cora and her husband, John DEVINE, in various census records. There's an IL marriage record for John DIVINE, age 22, to Cora F. LAMKIN, age 19, on 4-May-1905 in Marion Co, IL.Groom's parents were T.I. DIVINE and Tourra F. RIGGS.Bride's parents were Jas. L.F. LAMKIN and Mary PICKARD.
While Cora's marriage record lists her father as Jas. L.F. LAMKIN, her brother James' death record adn brother John's marriage record both list him as James A. LAMKIN.
There's an IL marriage record for John MCBRIDE to Mary PICKARD on 21-Nov-1867 in Clay Co, IL.I feel fairly certain these are George's parents.