Bro, I just messed up my pants
That is concerning, what happened with your pants?
My younger sister pissed in my pants because I wouldn't let her be on my lap.
Obviously, we all want to stay clean and keep our clothes in good condition, but don't blame your sister.  She sounds like she is too young to know any better.
It's her fault, she shouldn't piss on me. I can't keep cleaning my pants everyday.
If your siblings constantly pee on things, then you should see that she is wearing diapers, and see what you can do to help her proper potty training, and if your parents are around, you can try and tell them to teach your sister. I hope you resolve your problem and if you need help, make sure to ask your parents and they will be able to help you.