I'm using an Iphone 5 and I just tap the NPC's I want to talk to. There's the little feed back circle at their feet, tapping that should work. Sometimes zooming in as much as you can makes tapping these little areas easier.
Unless you're trying to talk your own NPC characters because the only personality they have is in your imagination
There's a minor selection bug on iOS that can sometimes stop you from interacting with objects that is manageable by zooming in slightly when it crops up.
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Unless you're trying to talk your own NPC characters because the only personality they have is in your imagination