Integrating feral with two best friends

I just trapped a feral 10 week old kitten last week in my backyard, a really cute little black and white . She was emaciated and probably wasn't going to last a lot longer. After a week in isolation in a large bedroom, she has gained a lot of weight, has become litter-trained, plays with cat toys, and has become incredibly sweet and affectionate.

I'd really love to keep her, but we have two 2-year-old cats that are sisters and best friends. They absolutely love each other - they're almost always together playing, napping, or just hanging out. They have never so much as hissed or growled at each other. However, after introducing the new kitten for just 5 minutes, in two separate sessions, it's clear there's a problem. Not only do they hate the new kitten, but the smell of the kitten makes the sisters question each other's identity. They'll hiss at the kitten, and then lose track of the kitten and start hissing at each other!! One of them even swatted at the other with a hiss. It was really heartbreaking. They go back to normal after a few minutes and don't hold grudges but I really don't like it.

I absolutely refuse to jeopardize their relationship with each other. But I wish there was some way to get them to welcome the new kitten without turning on each other. If their defensive, hostile reaction would relax a little, then maybe it might work, but I'm not too optimistic this is possible.

Any ideas before I try to adopt her out? She has really grown on me in the past week. Thanks for any suggestions.

I would try Feliway, and keep them separate. Slowly introduce them by scent first, then brief visual meetings, where you hold her and simply let them see each other without getting close. Slow and patient encouraging both sides. It sounds like you know whats best so trust your instincts!

its going to take time..I integrated a feral kitten and kept her isolated 3 days in a room and slowly let her out..alone at first whilst the others were kept away...then little by little..this will work..relax or all will sense your anxiety...