You have made the right decision on the clubs to place your bet on. With Napoli recent decline in performance, I don't think that they are capable of winning Juventus that are in their super form now. If they can draw with Inter in their last clash, I don't see why they won't be able to win Napoli that Inter win 3-0 three days ago.
Napoli have not been able to sort out their problems. I am one of the people who felt that the sack of the French coach Rudi Garcia would bring the desired turn around but I was wrong. I felt that Rudi was not able to unite the players to get the needed result like Luciano Spalletti. In five games Napoli has won just one and three of these games were played under the new coach Walter Mazzarri who has just won one game as coach of the club. Although I will not bet that Napoli will win this game I will never doubt the capacity of the club to beat Juventus because they have quality players that can be great threats to defenders. Napoli will want to put smiles on the faces of their patient fans, so they will put in the best.
Inter will definitely win Udinese because they already have a rival behind them, and if they should lose or draw any of their match, Juventus might take over the first position from them. Apart from this, Inter is stronger than Udinese and that makes it impossible for Udinese to win them.
Inter Milan is in top form and can beat any club in the Seria A, therefore I will not doubt that Udinese might lose the game on Saturday. Udinese is currently sixteen after gaining just twelve points in fourteen games. But I am not totally writing Udinese off because they were able to defeat AC Milan this season which means that Juventus should be careful because anything can happen.