Take your group into the Church and do the Stations of the Cross together.
Spend some time learning about Confession. What is it? How often should we go? How do you go to Confession? You can read up on confession in the Catechism of the Catholic Church (paragraphs 1422-1498) [...]
Take a meeting to discuss sin, what the Church teaches, about sin, etc. There are some great resources you can use to discuss sin. Here are few: Resources & Ideas CCC 1846-1876 Busted Halo Video [...]