Research, how does you Dad feel about the religion? Did your mum marry your step dad and then get baptised? Or was she baptised before they married? Women have zero power in this religion and must needs get it from the men in their lives. With a non believing mate she will be very low on the pecking order without a son, in other words YOU, climbing the ranks. Her motives are not entirely pure.
Is there any way you could show him JWfacts.com or some of John Cedars videos? Or JW support you tube videos? Or Susan Gaskins videos? Or exjw analyzer? Please try to get him on side, explain the way they use shunning as a control method.
I know EXJW Reddit has a big list of country by country help sites for mental health issues.