Can I drop off my friends and come back and pick them up? They don't have a car.

Yes you can. You can get a dropoff pass usually

If you are dropping off after 6 pm, parking anywhere is free. Before 6 pm, drop off at "guest drop off." See link for further info: https://orlandoinformer.com/universal/parking-transportation

Yes you can. There is a guest drop off site, near the bus stops. Just set on a pick up time and that's it.