Who are the letters really to?

While reading the chapter why I'm not where you are, I was having trouble figuring out who the letters were really written too. Before reading this chapter I had thought that Thomas was writing the letter to the other Thomas, his son, because he had left him. Then during this chapter I began to question this assumption. On page 208, it said "sometimes my had starts to burn and I am convinced that we are writing the same word at the same moment", this quote went along with my theory that Thomas is writing this to the son that he abandoned, but then on page 214 it said, “In the days and weeks that lead to my release, I looked for my parents and for Anna and or you”. This quote made me believe that he was writing the letters to Anna’s son now because just before that Thomas had learned that she was pregnant. I continued to read and on page 215 it said “your aunt had told me that she was pregnant, I was over joyed…”, this once again made me stop and think that maybe it really is to his abandoned son and not Anna’s son.

So I guess I’m asking who you think that these letters are written to? Am I missing something that tells us who the letters are really for, or am I supposed to be unsure?