One last thing...is this possible? My husband says it is, but I don't know. Can an adult cat's personality change due to the introduction of a new kitten?
It can if the introduction is rushed and is not allowed to evolve over time. Keep the two of them seperate not only to stop any fighting that might occur, but the new stray needs to be seen by a vet and cleared of disease. Here is a link that might help youIntroductions Please