Havana Brown kittens & cats in Ennis, Texas

Chaos refuses to use a litterbox and with our work schedules we don't have time to properly try and do something about it, he does well with our other cats except one. In the picture is him, his mother, and his sister. Almost a month ago we got the girls spayed and ever since he's had a hatred for only his sister. Everytime he sees her he growls, hisses, sometimes he even lightly lunges at her with the intent of starting a fight. Lately he just sits from a distance growling/hissing whenever I open the door to my room in which she's been confined ever since. Nothing we do is helping and his sister doesn't deserve to fear her own sibling or be stuck in my room. We also have 5 other cats who are fine, we need the space and he needs someone who can properly take care of him. He's a real big love bug and doesn't fight with anyone else, I'm unsure how he'll act with other new cats or new environment in general away from the home he's known. He's very food driven and will get into everything.