I like the idea of burning...but with the fires in So. Cal and elsewhere, be careful. Another idea is to shred the letters, or burn, but then, put the shredded pieces or ashes in some balloons. While this is not great for the environment, but sometimes, the souls and wellbeing of my munchkins override my desire to protect animals. By sending the balloons out into the world, talk to or write on the balloons then send them off. As they float away, let the anger, fear, depression, anxiety, everything else you hold inside float away w/ them. As they go, the power the aggressors had over you will also go. When the balloons finally come down, in some distant place, the balloons will decompose, and so will the ashes or shredded papers. Hopefully, some animals will use those spots to go to the bathroom, but that is just an extra sweet desire of mine.
Just a thought from someone who shares the memories and hopes to see this problem come to an end.....soon.