older established cat fighting with new younger cat

Question
We have three cats (2 males and 1 female) who have been in the household for years. Our son moved home and brought his young female into the House (all are fixed).  She was scared and has stayed in the basement on top of the shelves. He would take her to his room at night and then she goes back downstairs. The older female has been "hunting" her, with some fights. Today when Callie went to get on the shelves, Natasha was up there and waiting for her-huge fight. What can we do to help this situation out? Thanks.

Answer
well it is never easy having lost of cats living in such close proximity and this sort of behavior is a natural reaction to a new cat moving in on another's territory.

the best way to introduce cats to each other using the safe method but it does take some time and effort on our part as it needs time to give both cats confidence in each other without the fear of attack.

the method is described here

/introducing-cats.html

Other than that there is not much you can do, often these things are sorted out between the cats, with one cat becoming the dominant one.

I hope things settle down soon

best wishes Kate