Help stop the yelling

Lately my seven year old sister hasn’t been sleeping all night and my mom and her boyfriend get frustrated and yell at her or even sometimes make her stand in the kitchen or living room till she stops crying. As a 16 year old and her older sister I too get frustrated and only have to yell once and occasionally talk to her and then she stops. I hate when my mom and her boyfriend yell at her continuously and I’m terrified to tell them how I feel. How do I make all the yelling stop without going to counseling?