Puppies have sensitive stomachs & should be fed what they have been fed at the breeders. When I got my pup the breeder gave me a bag of the kibble that she had been on. It you want to change the food he's eating it has to be done very slowly to avoid tummy upsets. So it could be one of 2 things, you've changed his food cold turkey of it is in fact his eating the other dogs food. There's usually instructions on the bags how to change over to a different food.
Puppy can't control their bladders or bowels until they are older & its up to you to teach him where you want him to go. He should be taken out after eating/drinking, sleeping, playing & every hour in between. He's a baby just like a human baby.
He shouldn't be allowed any freedom in the house, you must watch him at all times & if you can't he should be in an easily cleaned room with only his bed, food & water bowls & a toilet area. If you go to the link I gave in your other post you'll find when you download the book what a short & longterm confinement areas look like.
http://www.youtube.com/watch?v=wsSsxU12xGU http://www.youtube.com/watch?v=FzXXf...eature=related