Cats Just Won't Get Along

I've had my cat Sadie for four years now, and she's a sweetheart, but she doesn't do well with other cats. Recently I brought a new baby into the house, my cat Tallulah. She's about a year old and has only recently been fixed in the last month or so because her previous owner didn't take care of her. She had a litter of kittens before she was fixed, as well.
It's been almost two months now since I brought Tallulah into the house, and she and Sadie still won't get along. They share the same food dish, litterbox, and everything else just fine, but if one gets too close to the other, there is a hissing, scratching, and yowling fight, and they get so loud! They're both declawed so neither can do any real damage. And I've been scolding them both each time they have an encounter, but it just falls on deaf ears. They're cats, after all. What can I do to make them get along? I'm afraid this will continue to go on forever, because things are not any better than they were the day I brought Tallulah home.

Hi ! Let me first try to suggest a better understanding of the situation and say that it isn't that "they won't get along", but that they don't get along. A lot could be from how they were introduced, some will suggest a reintroduction. At this point since it has been so long, I don't think this will "heal all wounds", but there are some things that can greatly encourage a more peaceful relationship if not BFF.
First thing I would suggest is 2 litter boxes and separate food bowls, this will allow them to respect each other more, if sharing it only increases intrusive and aggressive feelings and behavior. It is also very important that you have daily interactive playtime with them. This is so essential! Play with one in front of the other if they both have interest, both at the same time is the overall goal. Find a toys or toys that both have interest in and encourage a happy, playful behavior and mental state they can have in common.
It is also important to step in when they are showing signs of a scuffle, but to do so before it gets to the point of physical interaction. Scolding, as you said, does nothing for a cat but increase the negative or aggressive emotional state at the time. It is important to be calm but firm and assertive when stepping in. Clapping the hands, a quick but firm "no" or other vocal command that you only use to distract from a building negative behavior. I use "eh, eh, eh, eh..".......... If you interrupt the process of the frustration leading to a growling and then swatting, scuffle, you are hampering the negative interaction.
Good luck!

Another thing besides playing with them together - you can do is give them treats when they are close to each other. The idea is to have them associate being with each other as a pleasant thing.

They may never be best friends but with positive reinforcement they can probably end up like siblings and put up with each other without too much fighting LOL.

Good luck!