"Her uncle drives a cab."
Translation:Onkelen hennes kjører drosje.
I've never once heard drosje in Norway, just 'taxi'. I've only heard drosje in Pimsleur's audio course and here. I think it's an old word.
'sin' means that the subject owns the thing. The uncle cannot own himself, so there is another person (she) who owns the uncle. In which case you should use 'hennes'.