The biggest reason and you have not mentioned this at all is-Is his sister Ella spayed???
If not, there's your answer!! She is attracting unfixed males and Louis is guarding his domain. Whether he is fixed or not he still can smell when she is in "mating mode", along with any other unfixed males in a 2 mile radius!
BTW, once a cat becomes sexually mature they do not recognize siblings/parents, etc. like people do. They mate with anyone.
If not, there's your answer!! She is attracting unfixed males and Louis is guarding his domain. Whether he is fixed or not he still can smell when she is in "mating mode", along with any other unfixed males in a 2 mile radius!
BTW, once a cat becomes sexually mature they do not recognize siblings/parents, etc. like people do. They mate with anyone.