First pray for them (whether quietly to God or with them personally) that God would enlighten the eyes of their heart, pray that they may hear and see by the power of the Spirit. Then the way is more open, though I will not guarantee they will accept everything you say, for darkness does not like light. Then follow our Lord Jesus's way of explaining things, ask a question. A very simple one like, "Does God's anger last forever, but his love for a moment?" or "How would you feel if you had to watch your (insert family member) be tortured endlessly? or "Did Jesus fail in his role as Savior?"
Simply ask questions, then hit them with bible verses.