Hi Simone! In the first example, using "could" sounds like a question regarding your physical ability to pass through. Although "can" can also give off a similar connotation, it is more widely used and therefore sounds more natural. "Can I pass through, please?" definitely sounds better of the two, though the other sentence is fine as well. In the second example, the use of "shall" seems a bit formal to me. If you were talking to your dad, you would probably say something like "Should I go around him?" or "Should I overtake him?". "Go through" and "pass through" are not applicable in this second example because it implies that you're going to run through the other car (and cause a car crash in the process). Hope this helps. ~Andrew