Assuming the spare tire you're using is the one originally equipped with your vehicle, it should be load rated to handle the maximum gross vehicle weight your car is rated to carry on whichever corner of the vehicle it's installed. Manufacturers do this because if you were to have a fully loaded car and get a flat, you want the spare to be able to withstand the amount of weight in the car at the time (so you don't have to take stuff out of the car in the middle of wherever you got the flat).

So yes you can have 4 people in the car on the spare BUT you can't expect to drive the car very far on the spare. Spares are usually designed for a maximum driving range of only about 50 miles. Subtract however far you've already driven it from that 50 mile range to decide whether you can safely make your trip on the spare.

Yes but you need a jack and lug wrench too..

OK seriously where in the world do you live that has laws based on vehicle occupancy and spare tire requirements? I have never heard of such a thing - many newer cars don't even come with with a spare.

spare tire is up to you, not how many people you have in the car, but never drive without a spare tire

Oh man. Tough question. Let me think, let me think. I am going to go out on a limb here and say yes. You can have four passengers and a spare tire. As long as its not on a Wednesday.

Just don't drive in over speed with spare...

spare tire is for when you get a flat... nothing to do with the number of people in your car