FTB - I feel you. No matter how long I'm out etc., the anticipation of hanging out with a group of JW's is nerve wracking. Anticipation is usually worse than the reality.
If their motive is to reach out to you, think of a simple comeback to have ready. Psyche yourself up to be super positive and happy and ask about them/their families/work...anything...it always gets them off track.
If it's strictly a social occasion for lunch, go with the flow. Same suggestions as the above paragraph. For some reason being strong and sure and turning the conversation back to them has always worked for me. Crisis averted.
Good luck!