Your sibling can’t control what they say. Most of the time they say it because they don’t feel in control and want to have a little bit of paired to feel important. I have a young autistic brother an d he uses bad words and isn’t the nicest person but I know he loves me. I’m sure your sibling really loves you and probably looks up to you. Your like there big role model. Just don’t give up on them and always know your not responsible for them. You be you. Enjoy yourself.