You didn't mention where in Pennsylvania they lived, but the only Irene I could find who was the daughter of Charles is in the 1920 census. it shows Charles 34 with his children Eugene 9, Evelyn 7, Irene 5 and mother Louisa 56 living in Frackville, Schuylkill County, PA. All were born in Pennsylvania except Louisa who immigrated from England in 1879.
I could not find Irene in the 1930 census. I also could not find a Charles Witchey who was born in any place outside the U.S. Amanda could have been the daughter of William & Mary Ney from Beaver Twp., Columbia County, PA. coincidentally the Charles Witchey above was born in Beaver Twp. too. He was the son of William and Louisa Witchley.
If you know the names of your mother's siblings it might help in locating her in the census. Do you have any idea when and where your grandparents died? Basically if you could supply some more clues I might be able to find the info you seek.