Need advice on guiding my sisters back to Islam

Assalamu alaikum. I'm a uni student in the US, living with my two sisters. My younger one studies with me, and the older works at the same uni. Our parents are back home in the Middle East, but we visit during breaks. My older brother, alhamdulillah, is married and stays about an hour away-he's a solid practicing Muslim. About my sisters: the older one left Islam about 7–8 years ago and hasn't been Muslim since. Lately, she's been exploring religion, not sure where that'll lead. I still love her and treat her like always. She respects my faith and doesn't do anything against Islam at home. Only me and my younger sister know-she was the first one told. My older brother has no clue. My younger sister still identifies as Muslim but is really distant from the deen. She recently started a relationship with a guy from our uni, you know, like a boyfriend situation. Our parents don't know any of this, and I won't tell them-I want my sisters to share it themselves. I care about them deeply, but it hurts seeing them drift so far. I make dua in every salah, begging Allah to guide them back. I'm stuck, and this has weighed on me for years. I go about my days, staying positive, but it's always in the back of my mind. I need some guidance. I'm scared of being held accountable for their actions on Judgment Day and fear Allah's punishment for what they're doing. JazakAllah khair.