I voted to leave her and your father alone only because if they are not ready, everything you say could hurt your relationship. When one of my sister’s left the Catholic Church, she would get so angry at me mentioning anything to do with religion and God. There was a time I had her alone on the phone and she had many questions. I told her that I would write to her the answers for I had to go to work. I sat one Sunday from morning until night answering her questions, being careful not to mention anything to Catholic and only using Scripture. Well, about a week later, I get a call from her husband and he was angry. He was cussing at me and yelling at me for writing that letter. I tried to explain it was in response to my sister’s question and he would not let me talk. I was so angry that my sister did not call me herself if she was offended at the letter I sent her. I meant well and did not mean for this whole mess to happen. My sister’s husband told me not to call my sister or write to her and if I wrote to her that he would know for he opened all mail. She was not allowed to open any mail and even now 15 years married, she is not allowed to still. He is very controlling but she doesn’t see that. That letter and call from her husband ruined my relationship with my baby sister for 5 to 6 years. I did not speak to her in all that time, but not because I was angry at her, but because I thought I was not allowed to. If it was not for my mother calling me one day when my sister was at her house and making us talk, we would not have a relationship now. I did have resentment and unforgiveness for some time and a broken hurt, but that was healed in a healing Mass.
Becareful with your dad and your sister. I would advice you to witness to her and him your love for Christ in how you talk and dress and behave. Action speaks louder than words. If your sister should talk to you about something in particular about God and the Church, take it as God’s will for you to talk to her. I would talk than, but only than and now just bring up God in your conversation for the sake of converting her or him. I learned that doesn’t work. I do have two sisters who left the Church and thank God are not atheist, but we can’t mention to much about God for we believe in different things. But when an occassion presents itself, like when one of them was going to get a tubal ligation, I spoke to her the true. She didn’t like it and never mentioned it in front of me again and did it anyway, but she was informed.
The best thing you can do for your sister and dad is pray for their conversion and offer up sacrifices. I have a best friend who was an atheist for many years, but she had a good Catholic friend who prayed for her conversion and it happened. That friend prayed for her for 30 years, but my friend is a very devote Catholic and has been for more than 10 years. She is so grateful to her friend who never talked religion to her, but did tell her that she was praying for her.