Thanks for the feedback and support everybody, its much appreciated.
I really don't expect the letter will have much effect on their future actions, they are both very loyal JWs. They were baptised just before I was born 50 years ago, that's a lot of indoctrination.
The point really was that sometimes things just need to be said. They need to know that we don't meekly accept their unreasonable behaviour, it isn't natural and we do judge them for it.
If it has any positive effect on them that will be an unexpected bonus.
I think they will either not respond at all or my dad will ring and want to have his say. His only refuge is the old JW canard that I made the choice to leave. I hope he does because I am more than ready to discuss that one with him.