I have had some visits recently and I know the kind of frustration you are dealing with. I got much further with them than you - watching them be sooooooooooooooo sweet, when all the while I know what they are really like. It's galling!!! You are caught between a rock and a hard place. If you show them that they lie, they don't deal with the lie, they deal with how you know about their lies. They are then absolved from any further dealings with you because you are "apostate" and not to be trusted. Only an apostate raises the subject of their lies and they know they have the truth, so apostates are evil for trying to make the truth look false. You can't win.
Marilyn