Possibly silly question...
Did you have one potty or two (or three or four) when you potty trained your little ones? I'm trying to figure out the logistics of it all.
We're not hard core potty training yet, but we have two little potties plus one that goes on the big potty. I would definitely have two of something because of the "monkey see, monkey do" principle. If one wants to go to the potty, generally both want to and if you don't have two of something you'll likely have at least a fight if not a mess too. :-) All of our potties were hand me downs, but DDs are okay with having different potties. I have one that prefers "her" little potty and one that generally likes the seat on the big potty (I think because it's closer to the toilet paper!). We only have a one story house, but if we had two, I definitely think 4 would be the way to go. Apparently Ikea has some good cheap little potties.
***Twin fraternal girls born at 35w6d in 12/2008***