Dan,

The LDS Church website FamilySearch.org has some records that might have the info. https://www.familysearch.org/search/collection/list#page=1&a...

1) death records https://www.familysearch.org/search/collection/show#uri=http...

William John Jr is there and his death cert says Silverbrook https://familysearch.org/pal:/MM9.3.1/TH-267-11738-4499-13?c...

2) Delaware, Vital Records, 1680-1962 has records called Tatnall Tombstone Collection

https://www.familysearch.org/search/image/index#uri=https%3A...

Unfortunely, no Rothrocks https://familysearch.org/pal:/MM9.3.1/TH-1951-24449-20539-39...