You are correct that Annie Duvall had other siblings besides Grover and Wade - two other brothers and a sister.
Your grandmother, Annie, was the eldest of her siblings.She was followed by Laura, Brack, Wade, Grover, and Wayne.Following is the information I have on each of them:
Laura Duvall was born March 1884 in Virginia.I don't know when she died.She married Larry Emerson (I don't know any dates for him).They had at least six, and possibly seven, children.
Emet Brack Duvall, was my great-grandfather.Brack's daughter was my grandmother.Brack was born 2-6-1887 in Rugby, Grayson County, VA and died 4-20-1930 in Fairwood, Grayson Co., VA.He married Emeline Spencer 11-3-1906 in Grayson Co., VA.She was born 9-7-1888 and died 12-15-1955.They had six children.Brack was a minister in the Baptist church.
Wade W. Duvall was born 6-14-1889 in Virginia.He died 6-17-1968 in West Grove, Chester Co., PA.He married Mary Osborne.She was born 3-2-1894 and died 4-3-1937.They had three children.
Grover was born 8-27-1893 in VA and died in 7-24-1970 in PA.He married Lora M. Reedy (I think that's her last name) who was born in 1892 and died in 1966 in PA.They were married 9-16-1914 in Rugby, VA.They moved to PA in 1921 and lived in Lancaster Co.They had seven children.
Rev. Marvin Wayne Duvall was born 12-13-1896 and died 8-17-1984.He married Mary Bessie Walls 10-23-1915.Bessie was born 12-7-1897 and died 5-1-1993.They had six children.They lived in Mouth of Wilson, Grayson Co., VA.
The dates that I have for Annie's parents are:John Duvall born Feb. 1856 in NC and died Nov. 1900.Cynthia (Greer) Duvall was born 2-26-1856 in Rugby, VA and died 1-22-1920 in Grayson Co., VA.Her parents were Eli and Anna (Pugh) Greer.