Usually I'm pretty good at fixing problems with cats. Although I haven't completely run out of ideas just yet, I'm starting to feel a bit exasperated.
I'm going to back up a bit. Freya, my female is around 3-4 years old. We've had her for a little over a year now. I'm not sure if she's spayed (I asked the vet when I took her in for a blood-test, and she said they'd have to open her up to see, and I didn't want to risk that, since this vet has a very bad reputation with killing pets, and I only had money for the blood-test). Freya showed up in our back yard several times before we managed to catch her and bring her inside. She had been a stray for over a year, if not more, but she wasn't feral.
She took quickly with our male, Avery. He's a little over 3 years old, and neutered, since we adopted him from a foster-person at the shelter. Avery was reluctant to take to her, but I worked with him, and Freya was so friendly and sweet to him, that he soon took to her. It only took about 2-3 months.
My mom lives next door to me. A feral female showed up at her house one night, and we spent months trying to become friends with her. Finally, we did, and she had a litter of kittens. I procrastinated for a while in taking the last kitten, which was a female I called Mado. I was afraid taking Mado would disrupt the harmony in the house, and I was right.
Mado was born earlier this year; I'd probably say she's around 7-8 months old. I brought Mado in a cat-carrier first, and set her in the middle of the living room to see how the others would take to her. Avery seemed curious but cautious. Freya hid under my table, which is uncharacteristic of her. Mado was growling at them a little bit, but only because she was in the carrier and scared.
I have Mado separated in another room, but the trailer is small, so you can hear her meowing through the whole house. Now whenever Freya goes into the hallway (they have to go through the hallway to get to the litter-box which is in our bathroom; it can't be moved, because it's the only suitable place), she hisses at the door, or at Avery if he gets too close around her if Mado is meowing. She has slapped at Avery a few times too, but not with claws.
Freya has also been peeing on the floor in the living room, in the kitchen, and on our bed (she only peed on the bed twice), and on the couch. She's also been lying in the litter-box for a while. And hasn't been eating as much as usual. She's still eating, but not as enthusiastically as before. She seeks out the highest area in the living room to lay (but she was already doing that), and doesn't want to play with Avery at all anymore.
I've tried letting Mado out with supervision since she was dewormed last week. Whenever she is brought over to Freya, or comes closer to her, Freya hisses and growls. She also slapped at her, and when she was looking at Mado, Avery came up beside her, and she attacked him (no blood was drawn, thankfully). Freya still plays with me, though. She acts the same toward my husband and me, except she doesn't sit by me anymore when I'm on my laptop, but it could be because it's drafty where I stay.
I should have put things together. Freya is dominant. She is the one who mostly grooms Avery, and she seeks out the highest place in the room to sleep or hang out or eat. I know she's feeling threatened. Working with her the way I did with Avery when she was first brought in, isn't working, but every cat is different.
I'm going to get Mado spayed soon (by a different vet we found), and I hope that might calm things down. I will eventually start to let Mado out more and more, and hope that Freya eventually accepts her. If she doesn't, I'll have to find another home for Mado.
I'm sorry for this being so long. I just wanted to give ya'll all the information needed, so I can get suitable advice. By the way, the problems didn't occur at all until we brought in Mado. Freya used to be very easygoing and playful. It really breaks my heart to see her acting so insecure and unhappy.
Oh, and we've only had Mado for about a month. I know, I'm jumping the gun. I've read that cats can take months to even years to become friendly to each other, but I'm worried that Freya might never like Mado. Mado likes Freya, though, so that's good. Mado mostly ignores Freya when she hisses and growls at her.