Upvote:1
If I were you I would probably use the Venezuelan passport in Morocco just to avoid the confusion of having to present your incorrect Italian passport with the certificate. You can also show the Venezuelan passport to the airline, since Venezuelans do not need visas to enter the Schengen area. In other words, plan to show your Italian passport only to Spanish officers.
If anyone suspects that you will be staying in the Schengen area for more than 90 days, you can at that point bring out the Italian passport and the certificate to show that you are in fact an Italian citizen.
Therefore, I would answer your questions thus:
what document do I give to the airline?
The Venezuelan passport; if they ask about your period of stay in the Schengen area, also show the Italian passport.
Do I leave Spain with my Italian passport and enter Morocco with the Venezuelan one?
Yes.
Or do I bring the Venezuelan passport just for backup? If they give me problems with the Italian?
I would rather do it the other way around, as explained above.