Will a feral kitten ever tolerate a domesticated kitten?

We rescued Abi from the streets when she was about 6 weeks old. She is now almost 3 months. She's been socialized fairly good so far; she uses her litter box, is used to human voices and eats/drinks out of her food/water bowls accordingly. It's just, she's still very hostile to anything unfamiliar and tends to bite us on our hands/arms/legs/faces. Despite the bites, Abi is familiar with me and my family, so she always comes out in the open and even sleeps with me on my bed sometimes. As soon as friends come over though, she freaks out and hides under the sofa/bed until they are gone.

Despite spending several hours playing with Abi during the day, she still stays up for most of the night. For that reason, we decided to get her a playmate, Luka, who is about a month older than Abi, so he's 4 months old. Unlike Abi, who is frisky and bites literally anything, Luka is a lot calmer, and bites cat toys only, he puts his claws away and keeps his mouth closed when human hands or furniture comes near him.

I know that cat integration is a long and slow process (I’ve done a lot of research in order to ensure the two get along in the end), and for that reason I’ve set up a safe room for Luka that has cat toys, food, water and a litter box. I spend the majority of my days playing with him so he becomes familiar with the new people around him. At the same time, I make sure I play with Abi as well so she doesn’t feel as if she is being replaced. It’s been almost a week, and Luka has really opened up to me; he rolls over so I rub his tummy, he’s been sleeping with me ever since he came to our house, he enjoys being petted and he has licked my hand several times.

I started to switch their food bowls every now and then, so that the two feel like the scents of eachother are associated with good things (like food), and I’ve also rubbed a cloth on one kitten, and then let the other kitten smell it for some days, until I switch the cloths around again (so they’ve had time to sniff eachother’s scents plenty of times).

When I thought it was the time to let the two meet, with me supervising obviously, Abi hissed at Luka several times, growled and even hit him before we broke it up. When she was eating, Luka tried to join in but she started hissing at him, so she’s very territorial. For the most part, Luka has been the submissive one, not attacking back, and I’m grateful for that because he is a lot larger and could overpower her at anytime. Recently though, he tries to hit back, has hissed at her for the first time and even growls, so we quickly separated them again.

Now we’re back at square one; he’s kept in his safe room and she’s free to roam. The problem is that now that he’s seen there’s more to explore, when anyone opens the door, Luka tries to sprint out. The same goes for Abi; she tries to run into his room when the door opens, and sometimes when she gets through, they go under the bed and she starts hissing at him. He needs company 24/7 because when he’s alone, Luka starts meowing really loud.

We’ve decided to go back a step and allow them to get used to eachothers scents again.

I have this feeling that the reason for Abi’s anger is because she grew up in the wild, maybe her belief that everything is a threat will never worn off.

Can someone please tell me how to get them to tolerate eachother, or if they will ever be able to do so?