Well you have got a lot of great responses here. I have never been to either, but will be staying at Riverside in Oct. Our decision came down to FQ and POR as well, so I do know a little about the differences. We won't have children, so our circumstances were different, but from what I have heard and read, here are some of the pro's of each for 1 adult w/3 kids:
POFQ
~Resort is smaller and easier to navigate
~Dragon slide (though POR has a slide too, just not as "cool"

)
~First stop on the bus route (which is great b/c everyone should be able to get a seat on just about every bus..while we are at POR, we may actually walk to POFQ to catch the bus to MK..other parks, we are driving to)
POR
~Full service restaurant (don't know if that is important to them, but something to consider)
~Trundle Bed (not offered at POFQ, only in Riverside's Alligator Bayou section...with 3 kids, this can make a huge difference)
~Quiet Pools (if the main pool is crowded, there are always quiet pools close by...keep in mind that those staying at POFQ can use the POR quiet pools, but they have to trek over to use them)
~Fishing/Bike Rentals/Carriage ride are all at POR. POFQ can use them, but again, you have to trek over.
I don't know what is important to your brother and his kids, but these are some of the major differences between the two. The other obvious difference is the theme. Though both resorts seem to be absolutely gorgeous, my wife and I prefer the more rustic look of the Alligator Bayou section at POR. Good luck with the decision.