I would just tell them that you'd like to start a Bible study with them.
There are some wonderful Bible Study books on eBay.
Pick a Book from the Bible to study...one for every 2 weeks and discuss what you've learned from it...what each others interpritations are.
Keep a study journal too...each of you, writing your thoughts and questions.
You with the aster journal for your notes.
That sort of thing!
Have Fun With It!
Well once you get them interested in the idea, just hop on over to Amazon and find some Bible study guides for young adults or teens. You can also probably go to Barnes and Noble and look around. I used to go to seminary college and we had a womens bible study every week. We got the book we used as a guide from Barnes and Noble and it helped us with a week by week lesson and passages.
You can find a lot of studies at Lifeway and Family Christian Store, and probably Christianbook.com, though I've never checked there. Beth Moore hase many wonderful studies (can be found at these stores and their websites) that are specifically for women on different subjects/books of the bible, etc. Have Fun!!