Even though you control the copies, the ability cares about who cast the original spell when determining which other creatures that spell could target. If the original spell has a targeting restriction that refers to "an opponent," the copies will see that from the perspective of the original spell's controller. For example, if your opponent casts a spell that says "Destroy target creature an opponent controls" targeting your Ink-Treader Nephilim, its ability will create a copy for each other creature the original spell could target: the rest of your creatures. However, since you control the copies, all the copies won't resolve for having illegal targets.