major friend issues

Me and my friends went to this club the other day but it was being held by my sister's bullies and I didn't know that. I stayed and was pleasant to the bullies for the time during the club but afterwards told my friends I won't be going back bc they bullied my sister. What happened was my sister's bullies came to my house last year bc they used to be besties with my sister and were surprised it was average (they thought we were super poor) and it was nice. The next day they completely ignored my sister bc they got threatened by our house or smth and told everyone that my sister was a liar and a fake person. They spread the most dumb rumours but my sister's yr group was 90% rich white racist girls so they all ate it up. They told people that my sister pretended to be Indian to be exotic and that's super fake and total liar behaviour. You would think people with a brain would say that rumour isn't true but her whole yr group ostracised my sister and those girls made my sister's life a living hell. My sister had no friends for all of yr 11 and ran ASAP for sixth form. It gave her severe anxiety and depression. When I told my friends all this they refused to believe me. They said how can they turn a whole yr group against a super nice girl like my sister? They said the rumours they spread were super dumb how did anyone believe it? What my friends are failing to understand is that majority of my sister's yr group were racist and the people who weren't didn't bother to stick up for my sister. It's hard to understand if you weren't living through seeing your sister slowly deteriorate and I don't like talking about that stage in our lives when my sister fell into depression but they basically called me a liar. One friend is so determined to prove that none of this happened she's actually asking my sister's bullies which is super dumb. I don't know what to do. It's already hard to explain and talk about for me, but what my friends don't understand is that bad things happen to good people for no reason what so ever. They don't need to understand it, but I do bc I was there with my sister, but they're so desperate to understand what happened and it's annoying me. They don't belive what I told them essentially calling me a liar. What do I do?

Me and my friends went to this club the other day but it was being held by my sister's bullies and I didn't know that. I stayed and was pleasant to the bullies for the time during the club but afterwards told my friends I won't be going back bc they bullied my sister. What happened was my sister's bullies came to my house last year bc they used to be besties with my sister and were surprised it was average (they thought we were super poor) and it was nice. The next day they completely ignored my sister bc they got threatened by our house or smth and told everyone that my sister was a liar and a fake person. They spread the most dumb rumours but my sister's yr group was 90% rich white racist girls so they all ate it up. They told people that my sister pretended to be Indian to be exotic and that's super fake and total liar behaviour. You would think people with a brain would say that rumour isn't true but her whole yr group ostracised my sister and those girls made my sister's life a living hell. My sister had no friends for all of yr 11 and ran ASAP for sixth form. It gave her severe anxiety and depression. When I told my friends all this they refused to believe me. They said how can they turn a whole yr group against a super nice girl like my sister? They said the rumours they spread were super dumb how did anyone believe it? What my friends are failing to understand is that majority of my sister's yr group were racist and the people who weren't didn't bother to stick up for my sister. It's hard to understand if you weren't living through seeing your sister slowly deteriorate and I don't like talking about that stage in our lives when my sister fell into depression but they basically called me a liar. One friend is so determined to prove that none of this happened she's actually asking my sister's bullies which is super dumb. I don't know what to do. It's already hard to explain and talk about for me, but what my friends don't understand is that bad things happen to good people for no reason what so ever. They don't need to understand it, but I do bc I was there with my sister, but they're so desperate to understand what happened and it's annoying me. They don't belive what I told them essentially calling me a liar. What do I do?