If you are atheist and ex JW, would you accept any church invitation for you to explain what JW is all about?
Just because someone is athiest does not mean that they would automatically refuse to meet at a church.
Churches often offer their buildings for secular and educational events.
Why WOULDN'T and Athiest XJW participate if they were interested in talking about the subject?
I'm an atheist. But my oldest daughter goes to a private Christian school. We're very involved with that Church socially. Also, I enjoy various events and activities at the local Lutheran church, the United Church of Christ, the Unitarian church, and the local synagogue. I have a lot of friends in these churches and all know I don't believe. It's just not a problem.