Get some thick slippers and rub her bedding on them so they have her scent. When in the house only wear those. A lot of calm talking. Let her know where you are and that she's safe.
When she attacks, stop moving, talk her down. If you're able to sit down on the spot. At her level you're less...
If she is healthy and pooping with a more traditional stance, I would think a quirk of her own. Perhaps a learned behavior from others at the shelter. "hide as low as you can behind the box side so predators don't see you're vulnerable"
The 2yrs reaction afterwards will tell you if you need to worry. Does she hide and cower? Does she peek out curiosly? Does she walk around confidently?
It sounds like you want to keep this relationship and hope he matures and learns to understand what he's doing.
You could try the angle "I care for (or love if you're at that point) you. When you chase and terrorize my cats it hurts me too. They are my babies, when they are scared and upset so...
You're adult is very scared of the little invador. Give her some time and space. Make sure to wash your hands and maybe even change clothes after playing with the kitten. Talk calmly too her, don't push interactions, and let her come to you. She still loves you and is just overwhelmed right now...
The picture in your other post looks like you have a balcony. Can you put up a bird feeder?
Put on "cat TV" in the other room. You can find videos on youtube.
The idea is to get him distracted.
Many cats don't like to play with "dead" toy (things that don't move) and get bored with most of the...
It's unlikely. Kitten will catch up in size and it will even out. Get some cardboard boxes and cut small holes that kitten can fit through but teen can't. The little will have an escape if she wants it. Just make sure there are at least to entrances.
It sounds like he's chosen his person. Most of the cats I've met have a favorite person in the house but still like the rest. My Grandmothers first Siamese loved her and ran from everyone else.
Sqeeker, my picture, had a similar personality. After 15yrs he still ran if you glanced at him too...
I found things in the baby/toddler and dog sections for my Miss Monkey 30yrs go. She wasn't a chewer just destroyed all cat toys. Knocked something against the wall hard enough to break and dipped soft toys in the water to make them easier to tear apart.
Like @susanm9006 said todays spring...
The more they are together the better it will get. Your older boy is getting very worked up at the anticipation of playing with the kitten. You want him to be a little bored by the kittens presence.
It sounds like your teen already likes the baby and wants to play. An accidental injury is more...
Did your phone autocorrect for desex? She should let the vet know about him being missing and what you all have been observing since he got home. Ask the vet if it is safe right now.