Thank you for telling me about your situation. I went to a few pet stores in search of pet safe leather toys and didn't find anything, so I guess it's time to do an online order from somewhere. I've been letting him chew on the leather belt while I hold it every now and then - but I'd rather he have something kitty-safe of his own.
We tried the Bitter Apple when they were babies, and it didn't seem to deter the cord chewing behavior. But it's worth trying again, especially if it's not expensive.
He pooped in front of the basement door again.
I'm so confused. There are so many variables that could be causing it at this point - so we're making a list and changing them one by one, starting with the most obvious and least disruptive. I'm moving their food further away from their bathroom and we're implementing "play time" with the two of them in the evenings. There's a LOT of "social tension" between the two of them - they used to love each other, but now they kind of hate each other and won't even be in the same room at the same time.
So maybe he's marking territory? I don't know. And I don't know if the cord/leather thing is just making things worse for him, like it's stressing him out not to have that comforting thing to chew on.
So for now:
-get a pet-safe leather cat toy for him
-moved his food further away from his bathroom
-implementing play time with him and his sister in the evenings where we all play together and then they get treats
Thanks everyone for the advice. This is turning out to be a more complicated problem than I originally thought - I think this goes beyond the cord/leather chewing.