Ingenuous,
Many years ago, when one my siblings decided it was enough and all they could take with the religion and decided to leave, my parents tried all kinds of tactics and emotional blackmail with this one sibling.
She in turn kept her distance as much as possible. Never directly answering to any of their attacks. I remember my parents complaining that whenever they tried to reason with her she'd just wish them well and find any silly excuse to end the conversation politely. They'd write long letter that would just go unanswered.
She moved away and only kept in touch with the siblings that would be reasonable. I happen to be one of them. Thank God!
Years went by, and when the parents softened up and gave up their WBTS cause with her, she then came around more often and now they have a very nice relationship in which they respect one another and, much to my dismay, my parents don't try any religion talk or tactics with her. I guess they learned the lesson that it would only get them shunned by her if they did.
Hang in there. Be polite and patient. Distance yourself for a while 'til they learn the lesson.
DY