Ligonier and Greensburg are both in Westmoreland Co, PA.The prominent family there is PA93 and there are some matches, but I do not have your line. I do have a William F Fetter (born in 1872) who was the second of 11 children of David Fox Fetter (1841-1930) and Emma Noel who he married in 1870 (marriage #2).
I have nothing more on William F, but quite a bit on his siblings.
There are several other William Fetter about the same time, but he is the only William F Fetter on my lists.
Not sure if this helps.
I did not find a Lewis Fetter in this family.However, there is a Lewis Fetter who emigrated from Germany about 1885 who lives there, but there is no son William.