What I have are photocopies of letters, primarily from John Thompson. The start in 1861 and go to 1864 - they are clearly not the originals. Like you I am confused as to why my great grandmother had these letters. I have tried looking Joseph up on Ancestry.com but so far I haven't been able to come up with anything. I am hoping that two of us can collaborate and solve the mystery of why we have these letters. clearly they were important to my great grandmother and your family.
My e-mail is wlslack@hotmail.com. I would really like to hear more about what you have and what clues you've been able to figure out.