Possibilities - but did not find a census for York, PA in either 1900 or 1910 to indicate their parents? Nor could I find any marriage records of Milton to Mary Massonhammer or William to Buelah Yinger. Maybe you could locate the marriages with the town clerk?
U S Census, 1940 Ward 12, York City, York City, York, PA
Citing this Record "United States Census, 1940," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/KQZ9-C32
head William M Clark M 43 PA
wife Beulah I Clark F 48 PA
dau Phylis J Clark F 7 PA
stepdau Helen E Yinger F 27 PA
stepson Gerald E Yinger M 14 PA
US Census, 1930 York, York, PA
Citing this Record "United States Census, 1930," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/XHCX-CJQ :
head Milton H Clark M 40 PA
wife Mary E Clark F 34 PA
son George H Clark M 13 PA
daughter Flora M Clark F 12 PA
daughter Thelma I Clark F 9 PA
daughter Arnetta I Clark F 7 PA
daughter Evelyn M Clark F 6 PA
daughter Ada L Clark F 3 PA
daughter E Pauline Clark F 0 PA
U S Census, 1920 York, Pennsylvania
Citing this Record "United States Census, 1920," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/M6BZ-VJF
self Harry M Masenhamer M 46y PA
dau Gertrude ? Masenhamer F 17y PA
dau Margaret M Masenhamer F 14y PA
dau Alma C Masenhamer F 12y PA
dau Mildred A Masenhamer F 11y PA
son Paul D Masenhamer M 7y PA
son John H Masenhamer M 4y0m PA
dau Pauline E Masenhamer F 2y9m PA
dau Mary E Clark F 23y PA
son in law Milton H Clark M 31y PA
grandson George H Clark M 4y3m PA
granddau Flora M Clark F 2y8m PA
