Hey! This is awesome and it'll be cool if you can make it happen.
I don't think worries about piracy will be significant, but you can always check in with people before you play their game anyway.
I think a spoiler warning would be nice, but you're right that seeing an actual play won't render the game unplayable.
As for more than one game in a session, I thi k it could be done, but one would be sufficient. I'd suggest you try and pick two games that have complimentary themes if you want to do more than one.
I'm happy to send you a complimentary copy of either of my games (The Sealed Library / Fake Guru, Real Vice). You won't see the Sealed Library in the jam because it's one of two games thst came before the jam.