Cat food

I have four cats. One cat who is a year old, one that is 3 months and 2 that are 6 weeks old. I just recently got the the two younger kittens. I was feeding the adult cat blue buffalo wilderness indoor adult and the kitten hills ideal balance kitten. Well the kitten was eating the adults food and would in return eat the kitten if there was no adult, so I mixed the two foods. That was last week. Sunday I got the kittens and we got the petsmarts cheap wet cat food left that out overnight. Come Monday morning there was a big sized pile of soft poop on my bathroom carpet. Today, Thursday there was another pile of soft poop on the bathroom carpet and a small pile of hard kitten poop. I don't which food it was that made the poop like but we are planning on switching them to a different food tomorrow and we moved a litter box back into the bathroom.