When my husband and I both came out as Atheists, my brother in law was still Theist and responded defending his faith. When we talked, we talked mostly about science and we showed him some Neil DeGrasse Tyson and other related videos and he loved them. I don't think it was us that deconverted him, but the fact that he takes time to understand and learn and that did it for him.
The road to atheism is a long, lonely & stony one. About all I have been able to accomplish is to remove some of the 'stones' in people's paths.