Yes, I have written MANY letter to my mother - but as she died when I was 10, there of course, was no respond. HOWEVER - that was a blessing - I even went to her graveside, read it out, burned it, buried the ashes of the letter on the top of her grave. IUt helped.
Best bit - she could not reply!!!
I think putting your feelings, anger etc into writing is helpful - but as to whether or not to send it, I would encourage you to talk (a LOT) to your T and don't make a rash decision. I agree with the others - you need to be clear as to the purpose of sending it - if it is to 'make them realize' how much they hurt you, then it has the potential to leave you feeling even more disempowered. In a perfect world, they would read your letter, then break down and cry and beg for forgiveness, but as the others have said, the sick people who do these things to us are just not 'normal' people with 'normal' reactions. Most deny it, or even get to the point why deny it to themselves - they can lie to themselves and TOTALLY twist it in their head,s and sit there lying point blank and really CANNOT see they a) didn't ANYTHING wrong, b) you are crazy and imagined it, C) maybe know they did it, but either DONT CARE, or say you deserved it / it was your fault anyway. Or just as bad - say 'it was so long ago, get over it'.
Bottom line - it comes down to your expectations. IF you could sent a letter expressing your pain, but without ANY expectations as to their response, then it might help to send it. BUt if you were hoping for a response or for them to respond in a certain way, I probably wouldn't recommend it.
As I said - wiring a letter can be very very healing - but it doesn't have to be one you send.
The positives about writing a letter is you can express ALL your feelings - ALL your anger. You can use as many cuss words as you need to, call them all the names under the sun; and if it takes 5 pages or 500 pages, it does have an END. ESpecially if its pain or anger mainly you feel as you are writing. The pain and anger we feel FEELS limitless; but putting it down onto paper, it WILL have an end point - 5 pages or 500 pages later, you will reach a point that you have said all you need too. (Of course, that doesn't mean the feelings have finished, you may feel just as angry an hour later or a month later - but in that moment, it does have an end).
Another idea is doing the 'empty chair exercise' in therapy with your T. Imagine your abusers are facing you and sitting in front of you and you tell them exactly what you think and feel.
I've had many 'talks' in my head with my mother over the years - and i can IMAGINE her reaction, i can IMAGINE her saying ow sorry she is, and in my 'talks' I vary between having no mercy and continuing to tear strips off her, to reechoing the point of forgiveness.
With forgiveness, it is NOT about them, it is about YOU, There eis a saying "resentment is like drinking the poison and expecting the other person to die' - it only destroys us. My abusers that are alive (namely step mother), she desont lose sleep at night with any of the things she does. I on the other hand, lost a lot of sleep, hating her and wanting her dead. In the end, I hand to forgive her, for MY benefit. DO I accept what she did to me - NO. Do I lover her and want to go hug her? NO F#$king way; but I have got my anger to a manageable state, where I no longer have the utter hatred in my heart, and I sleep well at night. If she dropped dead tomorrow I'd probably feel relief (mainly cos I stand to inherit a couple hundred thousand $$$$ and i'm in financial need right now lol), but I would not had hatred in my heart about it.
However, 'forgiveness' is often WAAAAAAAAYYYYYY down the road - I am not suggesting you have to or need to even consider that right now; but later on, AFTER you've done a lot of your grief work, and healing, it might be a huge breakthrough for YOUR healing and peace.