1) The best way is to give them book such as “ Then I was guided” to read and then later on discus with them.
Link to the copy of the I was guided
https://www.al-islam.org/then-i-was-guided-muhammad-al-tijani-al-samawi
2) The only way to sort out any differences is to have friendly and open discussions on what you share in common as well as what is unique to each school.
3) We have our four main books but I would suggest your check this book of Ayatullah RayShahri:
https://www.al-islam.org/mizan-al-hikmah-scale-wisdom