I saw your post and thought I would try to help you. I do not live in IN but do genealogy. It took me two days but I found where they are buried.
They are buried in Sanders Cemetery in Lowell, Lake Co. IN West Creek Township.
Dates for Martha Ellen were 1835, and she died 08 Sep 1919 in Shelby which is in Lake Co. IN. Record is in Gary, Book H24 Page 35 for Lake Co.
There were no dates for Paul Williams. There were also their son, Edward R. Williams and Gracy M. Williams listed and their son, Paul W. Williams with dates 20 Feb 1909 - 09 Feb 1926. (Just a note: You have that Paul was born in 1837, but the 1900 census has him born Mar 1833.)
Hope this helps.