Really enjoyed reading your heartfelt letter. So many of us have been exactly where you are now. I thought about writing a letter too, but I didn't want them to later use it against me. I went to two elders houses and dealt with them one by one. Basically I told them verbally the same things that you wrote in your letter. I focused on the emotional, mental anxiety and distress that going to service/meetings was causing me. I told them I lost my faith in God and then I told them to leave me the hell alone and didn't want to have contact with them or any other elders again unless I initiated it.
So far it has worked wonders! They stay away from me for the most part( except for occasionally slipping the latest mags in my mailbox when I'm not home). I'd tell them verbally how you feel. I'd make demands that they stay away from you, and I'd stay away from topics that will ping their apostadar. Good luck!