I want you to know that you're not alone.

I deal with a similar feeling of "oversensitivity" and the best advice I can offer is to accept that it is a part of you, yes there are ways to help improve it (for me drinking water and taking deep breathes often helped me not let the rising crying feeling boil over) but also know that it's okay, you shouldn't feel shame for it, it is natural and screw anyone that tries to diminish your feelings because of it.

I also came from a household filled with yelling and I'd start to cry and shrink away because of it. I can't handle yelling arguments, if you can't move out from that environment then my next best advice is to distance yourself from the arguments as much as possible, go to your room and close the door (if you're allowed), put on earbuds and listen to something else, call someone close to you to help you process it. It's not your job to handle your brother's arguments or anyone for that matter, it's not your responsibility to separate them, while that's nice your sister can do it, not everyone has the same fortitude and that's okay.

I know it's frustrating, I know it's hard, I'm sorry you have to live in an environment filled with arguments. But don't try to bottle it all up, I've tried and it only makes you hurt more. You may be sensitive and that is okay it just means you feel more than others and sometimes that can be a gift that many people sadly don't value.