Someone should intervene, but for the sake of continued familial/friendship harmony, probably no one to whom the prospective author should ever miss speaking to again.
I also link you to SMBC's handy guide on "
How to Communicate with Writers", as well as "
Bad Review Bingo", for those of you brave* enough to try and tackle† the task.
* Or you could take the easy way out and passive-aggressively leave copies of this
handy Dilbert comic strip around, as many times as seem to be necessary to get the point across, if it ever does.
†
Morituri Consilium daturi te salutant, and all that.