Pamela, I have some information on the family you are searching for.Both Harry and Della died in San Diego, California.I don't know about Nellie except her marriage to Goley L. Shidler is shown in Delaware County, Indiana, June 24, 1907.The parents of Harry, and the two girls was William M. Ault and Annie E. Poorman.They were married in Belmont County, Ohio on March 8, 1874.My file note I've copied on below:
William's middle initial may be N.This shows on a Muncie Indiana Registry where W.N. Ault, T.J. Ault, and R.W. Ault are shown as the owners of "Ault Bro's and Co., a flour, feed and poultry business".This same Registry shows Wm N. Ault with wife Anna E., Thomas J. Ault with wife Charlotte, and Ralph W. Ault.There is also a Delaware County, Indiana birth record that shows the birth of a child to William Ault/Annie Poorman.I also found a California Death Record for a Harry G. Ault, born in Ohio, whose mother's maiden name was Poorman.
I have William's ancestors back to Valentin Ault, an immigrant from Germany in 1738.Hope this helps you some.