I am so sorry to read this.
My father was in a similar situation with me. My mother became a Witness around the time when I was born. I have some early memories about them arguing about religion and how to bring us up. But my father must have had a feeling that pressing the matter would just backfire.
I was told by my mother and other sisters to 'witness' to him, tell him to come to the meetings, play the worried daughter. But I really never did, I was never really outspoken. I hated it, when our mother told us not to tell him that we were going to the book study, but instead tell him we were going to play with friends. But still I have the feeling that this prevented me from having real conversations with my father, and a deep relationship.
My father was just really patient. He would od things with us as much as his work schedule permitted. Everyday things and fund things. I remember I was so proud that he let me help him change the tires of our car. When my mother was going out at night, we often looked at family pictures, and pictures when we were little.
He also was the one to encourage me to do well at school, to persue what I was interested in. He recognized even when I was in elementary school, that I had an interest and gift for math and logic. He would give me books on these subjects and magazines and articles. When I was older it was usually him driving me to math workshops and things like this.
No I am doing my PhD in math :-)
I called him not so long ago, to tell him, that I am not a Witness anymore, and to thank him. It was our first 'real' conversation, without anything standing between us. Since then, we have talked often and about a lot of things, and I really got to appreciate, how all these years must have been for him, what it must have meant to him to be so patient. I can't wait to go back home for a couple of weeks in two months.