I hope that Fred and Paul will be OK. See no reason not to. It would be "fair use", as this is your interpretation based on their creation, not a copy. In same fashion that it is fair use to upload and monetize let's plays on the net.
Unfortunately, that's not the way it works. Current copyright monopoly law in most countries does not allow the public distribution of anything that would be considered a "derivative work" of an "original
" creation, UNLESS you're making fun of it (which is why Mystery Science Theater 3000 is legal). The following books were censored (or prevented from being published) for similar reasons:http://questioncopyright.org/salinger_censorshttps://en.wikipedia.org/wiki/The_Last_ ... ion_status
Technically most non-commercial fan fiction is illegal as well. The only reason people don't get sued for it more often is because it takes too much effort for too little reward (plus bad publicity). Legally though, yes, non-commercial fan-fiction authors absolutely are breaking copyright law, unless their work is a parody (that is, unless it comments on the original work by mocking it. If it comments on the original work not by mockery but by more serious methods, then it's illegal).
Sorry for the dose of reality. I do hope that Fred and Paul give the okay for this project. (I also hope that the Peeru fanfic gets finished one day...)