Inter still has the upper hand to win the league because Napoli isn't consistent anymore. This is the only challenge that Napoli has. No one can tell if Inter will be strong till the end of the league and if that happens, it means that there's no hope for Napoli because Inter will win their matches. I can't tell of UCL, but based on their last match against Bayern, they have the higher chances of qualifying to the semifinals.
Inter can only win the the Scudetto will continue winning all their games or if Napoli drops points. Come to think of it, Inter players are more prone to injuries and fatigue because they are competing in more than one competition (Champions League, Seria A, and Coppa Italia ), while Napoli is just targeting the Seria A. Inter lost to Manchester City, the last time they were in the UCL finals. Winning Bayern Munich might give them the privilege of winning the UCL for the fourth time.