Last Night my Dream was about the sister of my Friend.
She died in my Dream. Today I woke up and i checked my Whatsapp. My Friend said, his Sister died. I thought first he is just joking and i went to see him and it was really true. I also had such a dream a long time ago but there it was about the Friend of my Dad and also about my cat, they both died. I don't know what to do and tbh i feel somehow weird. Like i'm the one who killed them. I didn't talk with anyone about my Dreams. I am really scared

It's alright. Whenever a person is about to die, someone will usually get a hint or foresee it before hand. In this case it was you. Sometimes you're barely related but yet you get these dreams. I think it has something to do with how pure your emotions are towards the person you dream about. I had an experience like that with my uncle. I was the first one who was notified in the family about his death anyway. And it's good you haven't told anyone yet. At this point, it will do no good. And it might also give you mixed responses by people, particularly negative ones.

These are only coincidences, what else could they be ?
Can you find an explanation about your killing them that makes sense ?

You're most probably dreaming about a lot of people, not all die.