I have empathy for you..
I personally believe senior JWs have believed for so long, it would shatter them not to live the lie, and or not associate with their child (unless they are easy going) which I don't think they are becasue of your fear of losig them.
Many families even in the world as Billy X mentioned stay away from certain topics for family peace, it's worth it. Unless you're involved in a project that could potentially out you.....why do it if the sacrafice is that great? If you can reason with your self you're side stepping out of love for your parents, it's easier to deal with.
The only true freedom is being away from that nasty WTS who enslaves people.
But if you must, I'd DA yourself, for some reason I personally feel it's better for two reason. DF always has a more negative connotation and when you DA you did it on your terms.
I still say mums the word, sometimes we are our own worst enimies......