Jenny, there is indeed a "family" grouping of Polley graves in the Gallagher Chapel Cemetery in Holland Township, Shelby County, IL (located a half-mile west & i mile north of Fancher, IL). However, the three people you are seeking did not have marked graves there in 1971-2, when the cemetery inscriptions were transcribed by Edward H. Boedecker (see his book, Inscriptions of Shelby County, Illinois Cemeteries, Volume II, first pub. 1972 & reprinted in 1980 & 1996). Perhaps your father and grandparents were interred after this cemetery was read; or, according to Mr. Boedecker, "There are quite a few unmarked graves, especially in the west half."
There are no Westenhaver graves recorded in Gallagher Chapel Cemetery. The Polleys whose inscriptions were recorded during the reading of Gallagher Chapel Cemetery are listed below, verbatim from Boedecker's book, pp. 31-32:
W. A. Polley
May 10, 1833 (no death date)
Sarah wife of W. A. Polley
July 12, 1842 - Nov. 21, 1903
Minnie B. dau of
W. A. & S. Polley
Aug. 15, 1873 - Dec. 22, 1890
Lenard H. son of W. A. & S. Polley
May 11, 1869 - Oct. 14, 1899
N. W. (Bill) Polley
1877 - 1958
Dora E. Polley
1884 - 1958
Harmon Polley
Aug. 21, 1902 - Oct. 19, 1938
God be with you till we meet again
Minnie Polley Abraham
Nov. 21, 1916 - Aug. 4, 1965
Everett Polley
1899 - 1971
Robert D. Polley
Nov. 10, 1956
Levurn F. Polley, Illinois Pfc.
Medical Department, World War II
Nov. 23, 1922 - July 29, 1945
Laura Polley
Aug. 22, 1870 - Dec. 4, 1934
Two next to above, no marks
Eddie son of F. & L. Poley
Died July 3, 1903
Aged 5 ds.
Mable dau of F. & L. Polley
Died Apr. 6, 1906
Aged 1 yr. 14 ds.
Two small stones next to above
No marks
There are a few other Polley (or Polly) graves scattered among other cemeteries in other corners of the county, but your father's and/or grandparents' graves aren't listed among them, either. Sorry I couldn't be of more help.