What an incredible opportunity!
You will be able to show them that you have not fallen away from God or the Bible. That you are kind and considerate. You will be able to show them, just by your life in general, that you are a moral and descent person. Leaving the WTS did not cause you to become a miserable and lousy person.
Most of all, you will be able to show them what a Christian really is!
I would take it slow and be a friend. Don't let them draw you into arguments. Merely point out and discuss things as the Holy Spirit leads you. You may be able to arrange a few more meetings, if you keep it friendly and comfortable. Don't come across as an apostate or opposer. Give them no reason to find fault with you or your behavior. You have a lot to offer. You are going to make a difference, I am sure! My prayers are with you!
Plant those seeds, Honesty!!! Plant those seeds!