AITA for refusing to help clean the bathroom because my brothers keep making a mess and my mom refuses to hold them accountable for it?

This is more of an are WE the assholes situation.

I (16F) and my older sisters (21F and 24F) shared a bathroom until the fall. My brothers (14 and 18m) have began sharing a bathroom with me when my oldest sister moved out and my brothers and 21f switched rooms which means my brothers now share a bathroom with me. I have expressed protest in this because my brothers are just too messy and refuse to clean up after themselves. The bathroom became messy quite easily and I have asked them several times if they could at least try to keep the bathroom clean. My mom would start yelling at me, calling me messy and how a grown woman shouldn’t live in filth. I kept defending myself dozens of times and I have even shown her the clean bathroom the second I was done cleaning, only for it to be destroyed in less than an hour by my brothers.

Guests are coming over today and I cleaned the bathroom the night before. When I woke up this morning, the bathroom was quickly messy again. My mom saw and immediately starts berating me and told me to clean up. I refused and said that my brothers need to help since the bathrooms was never messy before they started using it. My mom denied it and again said that I am a grown woman and I shouldn’t be filthy. 21f heard us talking and she joined in and said I shouldn’t clean as it’s unfair. My mom then went off on both of us and said it isn’t fair for her to clean the bathroom, not acknowledging or punishing my brothers for not helping to clean the bathroom clean.

I am now grounded for the rest of the weekend and had to turn in my car keys. My mom has been rolling her eyes and side eyeing me throughout the day.

Are we the assholes for refusing to clean?