You can by Puppy Housebraking Spray at Petsmart. They either haven't learned yet, or are being defiant. Use the housebraking Spray, and if that doesn't work, than use a spray bottle. Every time they go to the bathroom in the house, spray them with it, then place them on the pad and tell them that they are good.
I suggest getting them an Endoscopy. The vet will be able to view the stomach and colon. It can find digestive disorders and most vet hospitals habe this tool. When the dog is under anesthia, a flexible tube is insterted through the mouth or anus. It has a light and video camera on the end. It is a pretty minor procedure.
They may not know where to go poop yet. Put some fecal mader on the pads. So far, you are going about it right. Try puppy housebraking spray. You could also get them an Endoscropy, it could be a digestive disorder.
they might not know where to do their um....stuff. but if you keep doing the same thing, i am sure they will get the idea sooner or later. and we are hoping sooner huh? CHECK OUT MY DISCUSSION CALLED CONVINCING THE PARENTS!! I NEED ALL THE HELP I CAN GET!! :) :) :)