Should I tell on my brother?

So my parents found out my brother was smoking pot about a month or so ago and they took away everything from him, like his phone, computer, social life, car...etc cause he was smoking it in his bedroom by himself at night before he went to bed. then like a month later they gave him everything back but still dont really trust him so they told me to keep an eye out. well tonight i caught him smoking pot in his room and i dont know if i should tell. my mom said that if i smell anything that i should tell her but i want to be a good sister and not tell. we are going to maui in july and my rents said that if they find out he was smoking pot that he would not be able to go to maui. my brother has been begging me not to tell on him and swears he will stop but im pretty sure i will just find him smoking pot again in a bit. should i tell on him and risk him hating me forever or not tell and be a "bystander" and lie to my parents??