Here are the grandparents raising the brother who was 4 yrs older:
1930 CA Sacramento Co Sacramento city
Janzig John R head 57 married at 30 GERM GEMG GERM imm 1886 no occupation
Janzig Anna wife 53 married at 25 IL US US
Meagher Gordon grandson 11 s MT CO MT

1920 MT Gallatin Co Bozeman
Janzig Johonas? R head 47 m imm 1885 Na 1893 GERM mGERM GERM grocery merchant
" Anna E wife 43 m IL IN TN
Meagher Roslyn H stepdau 23 married(not widowed or divorced)MT IN IL waitress exchange cafe
" Gordon F stepchild(should be stepgrchild) 1 MT CO MT

1910 MT Gallatin Co Bozeman city
Janzig John R head 38 married once 14yrs GERM GERM GERM salesman hardware store
" Annie E wife 34 married twice 14yrs this marriage 3 born 2 living ILL IN TN
Dunn Moses stepson 16 MT
Dunn Rosaline stepdau 13 MT

1900 MT Lewis and Clark Co Helena
Callacott Edward head Jul 1858 married 16yrs MI ENG ENG
" Elizabeth wife Mch 1856 44 married16yrs 1 born 1 living NY IRE IRE
Dunn Moses boarder Apr 1893 7 s MT
Dunn Roselind boarder Jun 1896 3 s MT

WWII Army Enlistment
Gordon F Meagher b. 1918 MT enlisted 16 Sep 1950 MT

SS Death Index
Gordon Meagher b. 7 Oct 1918 d. Aug 1987 last address Punta Gorda Charlotte Co FL

WWI Draft Registration as of June 2, 1917 in Gallatin Co MT
Charles F Meagher
25 b. May 7, 1892
b. Denver Colorado
occupation RR Brakeman in Three Forks MT
single
causasian
medium hight
medium build
gray eyes
black hair
no other marks

1920 MT Missoula Co Lincoln
Meagher Charles E head 65 m MAS IRE IRE insurance agent
Meagher Rosemary wife 52 m imm 1874 Na 1887 ENG ENG ENG
Meagher Charles F son 27 CO
Meagher Raphael son 18 MT
Meagher Thomas F son 16 MT
Meagher Rosemary dau 10 MT


If you request Gordon's SS application it should verify his birth parents' names which would be the same as his sister. His mother's name should be Rosalyn Dunn and father is most likly Charles F Meagher.

Let me know if you have any questions. I hope this is helpful. This is not my family.