Headscratchers / A Wind in the Door

• Why are Sandy and Dennys so quick to disbelieve Meg when she claims that she and Calvin were inside Charles Wallace? Why do they denounce her as a liar? Wasn't Mr. Murry held prisoner on another planet by a giant brain in the previous book? Didn't Meg, Charles Wallace and Calvin journey across the galaxy with three angels in order to rescue him? Didn't they see the angels vanish into thin air right before their eyes? Shouldn't the twins remember all of this and be a bit more willing to believe Meg here? Or do they assume their siblings, their father and Calvin were all lying about their journey? Do they have their own, more mundane theories as to where their father disappeared for all of that time? Or are they Flat Earth Atheists who refuse to believe in aliens or the supernatural even it's right in front of them?