Two medium size woofers Vs One big size woofer

All other things being equal, all things are never equal.

Well, the first thing you need to do is make sure the smaller drivers move the same amount of air.  You can do a coarse guess-estimate by computing the area of the cone using the diameter divided by 2, squaring it, then multiplying by two.  A more accurate formula is using the volume of the cone - google it to see how to measure and compute it.   However, once you have the two areas the same, you will find the smaller drivers are much more expensive than one larger sub.  The advantage is smaller can mean faster and better resolution.  The disadvantage is they have to be matched otherwise it might blur the wavefront.   If the drives are in one speaker, then one could assume the manufacturer has matched the drivers.  For your example here, one would need about four  5 inch drivers to about equal one 10 in terms of moving the same amount of air.

IMHO I think the 2 smaller woofers would present a better mid bass quality with a little more dynamics. While the one larger woofer would provide a lower frequency sound but perhaps not as dynamic.
That being said, 5" woofers are pretty small.

ozzy