Irfan has the best economy in this tournament with it being under 5 which is extraordinary and he is only selected thinking about T20 WC, if he wont perform in Aus than obviously he will be out. Ashish Nehra was also selected in similar scenario by India for 2016 T20 WC.
Coming to Irfan jnr, I doubt he will get a match unless Abbas gets injured. Though I would have preferred either Ehsan Adil or Sameen Gul as covers for Abbas but I think management wanted more experience with 2 debutants and Shaheen with 3 matches.
Iftikhar’s selection is pretty simple. Considering Shaheen is coming of from deangue and Musa and Naseem ball with such pace and energy and their bodies are still developing so it would have been bad move to over burden them with just 4 specialist bowlers in the playing xi. Iftikhar is a decent batsman with 11 100s in FC and decent off spinner to keep things tight and to ball against lefties and in the mean time give rest to the pacers. With him Pak can also go with a 4 man pace attack if required.