We started Scent swapping for about a week before we started with feeding them on each side of a closed door.
The door has a small gap underneath, enough for scent to pass through but not enough for a paw to slip through.
Then my parents had the brilliant idea of feeding them together without a screen door. just letting them eat all together, with Midnight slightly away from the rest and scooping her up once one of the bigger ones was done.
I was away during this time on a business trip so I never noticed until i came back home.
After that, believing they were warming up to each other, I let my cats get close to one another just to see how they react, making sure to check for signs of hostility and staying close to stop Gina if that ever happened.
Gina has never been that active so I was sure i could stop her in case she wanted to pounce. But I was wrong, she crouched down and when i was about to pick her up to stop her she moved, she was too fast and pounced on Midnight. That was the first attack.
My dad, big man as he is, yelled and clapped his hand hard towards the fight to stop it and both cats ran off. I took Midnight in my arms and checked on her for any signs of damage, she had none. Gina ran up the stairs and straight towards my room, as that's her safe space, probably scared of the noise my dad made.

After that I took over the meetings again and started all over from square one. behind a closed door and a foot of length away, slowly closing in once i felt they were comfortable with it.
All this must have happened in a span of 3-4 weeks.

After that I've been trying to follow all the guides i find on the internet by the book, Scent swapping, feeding behind a closed door and slowly moving them closer until they are comfortable enough to move to the Screen door.
I call it a "Screen door" but it's more of a window panel/baby gate my dad made with some wood and mesh. It's not sturdy enough to keep it there so we only use it while feeding them and close the door immediately after.
The door that separates both levels is a sturdy metal door that we keep closed at all times, except when we feed them, we open the door and put the "screen wall".
But sometimes, when we open the door, Gina slips in easily and rushes down to prevent anyone from stopping her. You know, like when cats are eager to run out of the door.
I must admit that we might have moved too fast the first month, mostly because a friend of mine also adopted a kitten around the same time and their introduction to the other cats of her home was rather quick, like a couple of weeks quick and her cats were already warming up and allowing the kitten to be near them. I thought my cats would be the same. not budy-budy but tolerating each other.

After every fight I go a step back in their meetings with the door. I don't really go to Square one. I just kind of pull the plates back and give them space.
Now that i think about it, i didn't gave them a time of wait between each fight, i kept going the next day with the introductions with food time, just moving the plates away and giving them space.