Hi, this is my first post-great site!

To answer a part of your question no one touched on, I think Fredo went with Neri under the impression Neri was his friend. You can obviously see that Fredo was friendly with Neri, like at his mother's funeral, Fredo sees Neri and says, "Hi Al." So IMO, he went under the assumption Neri was his friend (Neri kept his friends close and his enemies closer ).

Also, I do not believe Connie would help Michael kill Fredo; but I do belive she realized it by GFIII.

Hope that helps!