After she’s been fixed and you’re ready to start introducing them get a Feliway diffuser. I’ve heard great things about them.
Right now, however, she’s in “Protective mama” zone. To have a male cat come into her territory when she has just had a litter is asking for trouble. Unneutered male cats will kill kittens to cause the mother to go into heat so he can mate with her.
StG
Right- get them fixed, try Feliway. The spray works OK too.
There is not necessarily still hissing, howling, and fighting. When I was young we took in my sick grandfather’s declawed kitty and one of our cats terrorized him, clawing him to the point of bleeding etc, even figuring out how to lift the latch on the cellar door to go after him. Since we were still bringing declawed kitty to see my grandfather, giving him away was not an option, and Mom was very attached to our cat as bitchy as she was being right then. So our cat got declawed too. There was never another fight again.
However, if the cat tolerates having her paws handled without ripping you to shreds too, OP, try Soft Paws instead first since nail caps are now an option that didn’t widely exist in the 90s. They last 3-8 weeks, and that might be enough time for momma cat to get her shit together without needing a more permanent solution. They worked really well on one of our later cats who enjoyed kneeding with claws out.
Not necessarily - you’re right. I was a little hot under the collar when I wrote that, and should have said “could”, instead of “would”. In my experience (friend’s cats), declawing did nothing to solve the underlying problem of the cats just flat-out hating each other. They went from swiping at each other to biting one another. Eventually, she had to give one away. Obviously all cats are different, YMMV, etc.
Haven’t read all suggestions, bt here’s what I’ve come up with:
Sometimes the declaw isn’t the worst option.
Okay, from the comments here it looks like my plan is to (of course) keep her up here until the kittens are grown enough to leave. Afterwards, she’s getting spayed for sure. I will keep her up here for a month after that so she can heal up and get her hormones under control.
I’m fortunate that she will let me touch her anywhere so I will get the claw caps for her as well.
I really wish the screen/glass door option was possible. I’ve seen that on My Cat from Hell. Unfortunately it isn’t due to the layout of the house and, well, the lack of screen/glass doors. 
I’m looking at the Feliway. I’m interested in trying it but reviews seem to talk more about it dealing with the problem of urination/spraying. Have any dopers tried it for territorial/fighting problems?
As I’ve mentioned before, she tolerates my sister’s cat but absolutely loathes my brother’s. I cannot figure out why. Maybe because my sister’s was already here when she came, and my brother’s is like an interloper?
I guess right now it’s the waiting game process. Can’t really do much but keep her up in my room with her babies and just go from there when it’s time. Thanks for the advice, guys.
We used a baby gate. Bought it cheap at a thrift store. Put the food dishes on either side of the baby gate, but just out of paw swipe distance.
I was thinking about those as a possibility, glad I’m not the only one! 
I’ll give these a go as well. Thanks!
Currently introducing a new cat and we tried the baby gate but the cats just leaped over them. <sigh>
The big problem is that my cat (the one who loves me only) is super jealous of new cat and pretty pissed off at the whole situation.
I think you may have nailed it, right here. Cats can be very territorial, and possessive.
I know this will happen for sure with my cat. I think I’ll have to get two and put one atop another. Hell, she may even climb them, it wouldn’t surprise me.
I’m still thinking of where I could put them. House is a tiny bungalow with one main hallway that has multiple entrances, no good for gates. Maybe block off a room but that’ll be a challenge, taking the gate(s) up and down every time. Sigh…We’ll see.
She’s pretty desperate to get out. Not that I can blame her, she’s been a stray all her life and now she’s cooped up in the attic with me and her kitties 24/7 for the next 2.5 months. Whenever I go downstairs she tries to zoom right past me. This morning she did it, went straight for my brother’s cat. I opened a window for her to perch on and get some fresh air.
The whole situation is frustrating. It’s my fault for being dumb and not even thinking of the possibility that this cat wouldn’t get along with other cats since she’s fine with my brother’s and is great with humans. If I knew someone who was looking for a cat, I’d happily give them to her. I don’t want to just boot her out onto the street. I hate playing the waiting game until I can get her spayed, buy the gates and the feliway but that seems all I can do right now. But now that I think about it, I could get the claw caps right now for some damage control!
For best fit with those caps, a nail trim is in order. If she’s amenable to nail trims and you can get them relatively short without quicking her, you can forego the covers and just trim weekly.
One idea, cheap under $50 wood framed screen doors can be had at Home Depot type places. They have a tension frame that fits inside the existing door frame. Either install it on the other side of the existing door so it opens the opposite way, or take the existing one off the hinges temporarily if there’s no room for an opposite - opening door. Really much easier than a baby gate.
You might come up with a cardboard box that would take her a minute or two to escape - put her in it before leaving the room and closing the door behind you. Does she bolt when you enter, or just when you leave.getting a screen door and building a box 15" deep just inside the door and putting the screen on it (self-closing) would create enough of a hall to hold a cat - rig it so she can push it open if caught inside