No idea how this would work, if at all, but would an intelligent item be able to ego possess a construct in possession of it?
Ego possession requires a will save from the one with the intelligent item, but doesn't call it out as anything regarding a mind-affecting effect. It's just a will save vs the items ego. Which technically a construct would have to save against.
That then being said, would the item then have control over something like an unintelligent construct while it is on its person with full autonomy?
It looks as if that is exactly what would happen.
Same thing as when a Cutlass Spider incorporates an intelligent weapon into itself... you get an intelligent Cutlass Spider controlled by the "mind" of the intelligent weapon. Cutlass Spiders are, in fact, Constructs.. so we have a pretty good example to use for this very thing.