A question for the native English speakers?

(Is it possible at all to make that question mark go away? I can insert my own question marks when I need them.)

I need some simple native speaker’s judgements on two sentences, for a semantics assignment.

Suppose we’re talking about three people, let’s say Ines, Garcin and Estelle. They all want to read one specific book, but not the same book. Ines wants to read No Exit, Garcin wants to read Hyperion and Estelle wants to read The Hitchhiker’s Guide to the Galaxy.
In this situation, if I would say “everybody wants to read a certain book”, would that be true?
I know it would be true if all three would want to read The Hitchhiker’s Guide, but I want to know if the other reading is possible too.

Another question:
In a context consisting of a number of guys who all have mothers writing books but who are not siblings, does the sentence “everyone wants to read a certain book his mom wrote” make any sense?

Thanks for your time.