Cannot remove door knob -- totally inaccessible!
You should be able to trip the latch, if you can see what you say you see - there should be something coming from the latch side which can be pulled or manipulated (often rotated, as that's what the knob would do) to do that.

If the hardware is really fouled up, a slim prybar next to the latch between the door and frame will often find enough flex in the framing to free it up, or allow you to pop the latch with a butterknife or the like, without major damage.

When you pass the point of caring about damage, the prybar nearly always works, or opens the way for the less slim one that does.

As you have the hinge pins out, beware of the door falling over when it gets freed up.