Need help with diffusing family drama between my twin sister (24F) and older sister (28F)

Family drama, need advice

So me, my twin sister (who has autism), and my older sister all live in our parents house.

My older sister yells at my twin sister a lot of times for things because she sometimes doesn’t understand them and because of that, my twin sister doesn’t say a lot sometimes. Recently the day before my older sister’s birthday, my twin didn’t want to talk to my older sister. On the day of my older sister’s birthday, my twin told everyone that the reason she didn’t say anything to anyone was mad because she failed a class in college. She didn’t want to tell anyone because she didn’t want to make anyone mad. Everyone was saying it was okay, and we went on our business. My older sister, however, was clearly irritated and didn’t want to speak to anyone for the rest of the day now because of this.

My older sister thinks that me and my twin get all the attention of our parents and she never got the benefit of the doubt and because of that she gets angry at me and my twin all the time. I just don’t know what to do in this situation. I just want to yell at everyone and just tell them to grow up or something. I feel trapped. What do I do?

Tl;dr: my twin sister and older sister are angry at each other because of family history and other factors and I don’t know how to diffuse the situation. How do I solve this?