See Adams Forum Message 4833.This message was posted by Dorothy Griffith, author of Adams Families of Southeast Kentucky.
This book has extensive information about Letty Simpson and John Adams and their relationships with the other members of the John Hobbs Adams family.
Regarding Samuel Simpson, there is a note(page 31) that says "She was a daughter of Samuel Simpson, a neighbor whose land bordered on Adams property" on Roaring River. Lydia's mother is listed as Mary Swain on Family Group Record No. 11311 (page 34)