Cats fighting

I have 3 cats. 2 females ages (16&11) and one male (8). We originaly had only one cat the 16yr old female but we later aquired the male cat through a friend who was moving and coudn't take him with her. At first my original cat HATED the male cat but after about a year she started to accept him and now I even find them sleeping next to eachother. So about 3 or 4 years ago we got the other female cat also through a friend who no longer wanted her. When we braught her home the other two cats really did not like her. The other female cat will go out of her way to scratch and chase her around. It has been atleast 3 years now and the other two cats still hate her, sometimes they will gang up on her and they will both chase her and corner her somewhere. The older female and the male cat get along just fine and they never fight with eachother but they both torment the other cat. I feel bad because the younger female can be sitting on my lap and she's all happy but than one of the other cats will come into the room and she runs in fear. She spends most of her time in hiding from the other cats. Does anyone have any suggestions on how I can stop the other cats from being so mean to her ???

Thanks

Perhaps try with Feliway? The feromenone of friendly cats?

Then of course the nr 3 has a lot of places she can go to. You build in shelves high up and so.

This is a tough one! It has been a long time for them to adjust to each other so at this point it would seem pretty futile to try to force a relationship when it is simply not going to happpen! Possibly you know of some one who could give her a home of her own, somewhere she's not threatened.