I have had multiple cats for years, the only problem I have ever encountered when adding a new member to the family is trying to bring in an adult cat. By getting a kitten whether it is male or female does not make a difference as long as the cats you have now are fixed and the kitten will be fixed at 6 months.
A kitten does not threaten the hierarchy of the household, although they do tend to liven it up. Just be patient it may take a few weeks for the older cat to figure out that the kitten is not going anywhere and will eventually accept it. You will also need to keep an eye on the two of them, so the kitten isn't too irritating and the older cat isn't too grumpy!!
RESPONSE:
We totally agree 100%! Thank you so much for your comment!!!