Why would our adult dog poop and pee in our house?

After we got a chihuahua who knows how to go outside put kind of still does it inside... He just turned one. She is a four year old cane corso who has always gone outside till now... Is she jealous?

If he kind of still does it, he's not fully hosue trained. Your other dog needs to be reinforced as to when to potty and poop too.

Don't assume sudden changes like this are always behavioral first...often there are medical reasons that cause these symptoms, so it's best to have the vet clear her before you begin behavior modification. She may also be smelling accidents that the Chi has had that you've missed and responding accordingly (when a dog smells "markers" from themselves or others it triggers a chemical reaction in their brain to mark as well...it's clearly easier to miss a Chi's accident than a Cane Corso, so she may be getting blamed for a problem that started with the Chi.) To assign "jealousy" to a canine is anthropomorphizing them...this isn't a canine tendency and may more likely be territorial since your Chi is no longer a puppy, and she could feel the need to lay down the boundaries and reinforce her position as alpha.Could be several things...best to get it straight before you begin corrections that could make matters worse. If you're unable to assess the situation completely, maybe call in a professional trainer for at least one session to assess for you and instruct accordingly, after the vet has cleared her first of course.

Could be jealousy but if all your older dog sees is the little one getting a lot of attention when he pees inside, she might think it's the "good" thing to do. When you clean up the pee of the chihuahua I would suggest quietly and methodically putting him outside to let him know that's where that should happen, clean up without a fuss - making sure not to make a big deal out of it in case your older dog gets the impression that it's fun or a game - just ignore them until it's all cleaned up.