Since your wife has decided for BOTH of you to go to the elders with a private matter without your consent, thus putting your life in front of the elders, without your consent, thus putting you in an untenable position, without your consent... let her go to them without you. Let HER sit there in front of three MEN and lay bare her guilty soul about your premarital sexual relations if thats what she thinks she needs to do to have a clear conscience or whatever her motive is for doing this. She decides FOR you to throw you both under the bus. And obviously has told OTHER people and not YOU she was going to do this. Since she approached them alone...she can go sit in the hot seat alone.
But as for you...its time to take your life, your heart, your conscience into your own hands and out of the hands of the cult leaders to whom you owe NO allegiance. Fuck their judicial committee!
Write your DA letter, and when the elders come over, hand them the envelope, grab your coat and tell them it's been a slice and you will return home after they have left it. And say to your wife... "Oh and honey? Dont forget to tell them about the blow job you gave me in the coat room of the Kingdom Hall."