It'd be easy. Just tell them they were right about NASA being behind everything, but not in the way they thought. This whole time they've been working with the Annunaki to hide the truth until such a time the Annunaki think humans are ready for it. It is now that time and they've chosen a select few to be invited to Nibiru to learn, return, and provide the humans with the truth. Their lifetime wealth will be taken care of, of course, as payment for their year spent on Nibiru.
Once out of orbit, we turn off comms and tracking and go on about our days.
This is very similar to a plot point in the later Hitchhikers Guide to the Galaxy books. A civilization manages to convince all their hair stylists, project managers, telephone sanitization specialists, etc that the world is ending and that they've been selected as the elite to be the first on the colony ships leaving the planet.
The original post is correct tho. As for the one claiming they were christians... More or less. Nubia was christian at one point, but much later than when those pyramids were built, in the 5th century. Meroe was no longer their capital and they were then called the kingdom of Makuria.