I am sorry for your loss.
Writing is a good way to express your feelings, and to retain your memories. Perhaps it will help you too, if you went to a beautiful place where you could read your letter out loud. Kind of a memorial service held by you - for your favorite uncle.
I understand your feeling of not wanting to subject your children to the shunning. But if you feel you need to pay your respects by attending the funeral ... You must go. The JW's may not talk to you - but that is of no concern, the funeral will be between you and your uncle. Perhaps you can find someon to watch over your children and just take your hubby with you. What ever you do - remember and make sure it is what you feel good about.