I would not use four jack stands because the lateral stability of either end of the vehicle is only provided by the width of the stance of the legs of two jack stands, worst for those 3-legged types or taller ones. If everything is perfect, knowing the car's weight you could calculate the tipping force required from a lateral push at one end of the vehicle.
But if there are imperfections in the geometry, the stability only gets worst, never better.
The geometry could be compromised by a number of factors that are not easily noticeable and can add up - poorly-centered placement of load, bending or flexing of the welded seam (if used,) soft, slightly uneven or sloped concrete base, and of course clearances and tolerances in the jack stand design that affect the load being centered perfectly over the feet. Never mind the additional loads from wrenching and opening doors, etc.
I get the creeps driving by houses with a car on four jack stands in the driveway, knowing that a small lapse in judgement could be fatal. If you're going to do this and work underneath, have a Plan B.