I don't get it. About Sieg's Skeleton.

This is one thing that I don't get. آپ know the Skeleton that was in front of Resha's 'fake grave right', and the manga کہا that is was Sieg right?. But I don't get this it's confusing me a lot. When Sieg, Elie and Haru were in front of the grave the skeleton was there right? but that was Siegs skeleton and he is right in front of his own skeleton. So does that mean that the skeleton is his past self یا that his future self actually went back to the past, یا is it that when Sieg stayed in the time arc یا whatever it's called, in the present time he is dead? Plus the letters that he sent from the past, was is actually in present time that he sent it یا is it actually 50 years پہلے that he sent it? IT IS JUST SOOOOO CONFUSING!!!! PLEASE HELP!!!