I agree with andy. I took in a female cat just over 2 yrs ago and now we have an uneasy truce in the house. I had 2 older females (they're 10 yrs old now), sisters , one of whom hates everybody except me and my GSD bitch! The little stray had kittens, 2 of which I kept and they & their mum get on fine with one of my other cats (she's always been very laid-back anyway), but mum and the other old lady absolutely loathe each other! They have this arrangement, they just avoid each other, but when they do come into contact the fur flies (literally!). Despite this, they come home at night & curl up in their respective places all over the house and no-one's left home yet. Persevere - they may never be best of friends, but they can learn to put up with each other!! K xx