What I found: Thomas married Mary Casey who died in 1889, then after she died married Alice Cadelia Johnson and after she died in 1905 he married another Mary ____.
With his first wife he had 3 children:
JJ O'Brien 1882-1918 married Julie. Had Walter Earl, Rose Marie, and Henry George
Mary Ellen O'Brien 1883-1974 married Jacob Taecker. Had Florence Rebecca, Ethel Mae, Roy Thomas, Hellen, Roger, Marie Elizabeth.
Eliz. Anne or 'Bess' 1885-1919 married Ted. Shank. Had Alice and Frank Shank