Barcelona will definitely beat Napoli, Walter Mazzari is not even the man for Napoli, this are just try and error coaches, for long term, you need a better and tactical genius for that club.
the situation might be different when Napoli's performance is like last season, with the same players and coach. but the situation is different, Xavi and the Barcelona squad will be more favored to win in advancing to the next round.
The tightest competition is probably Inter's match against Atletico Madrid. and there is a possibility that the last 8 rounds will bring together strong European teams who are favorites in the Champions League.
As the defending champion in La Liga this season, Barcelona is in a worrying phase, Xavi squad is a little unstable at the moment. However, Napoli fate is even more worrying, as defending champions in Serie A they have lost the opportunity to defend it. The current relevance to UCL matches is their performance in their respective domestic leagues, although it cannot be used as a complete reference, it can more or less influence their chances of winning.
I think Barcelona will have greater luck, I mean Barcelona chances are better and I predict Napoli will lose their chance to advance to the quarter finals. Of course, surprises can also happen, especially since the match will be held in February, both Barcelona and Napoli have plenty of time to improve their respective squads.
Regarding the Inter versus ATM match, yes, it is a match that is difficult to predict, because both clubs are fairly consistent. Statistically, Inter are better at the moment, considering that they were also runners up last season.