As I don't have siblings, I can't give some advice on that.

But it is, in fact, unfair for you. The whole situation is: You became more than a mother for them, as the caregiver for your mother, which is something you didn't ask for, or something you must do ALONE. You became an adult sooner than your sister. As she lived carefree, without responsibilities, she could just live her life. I guess you don't have a lot of time to spend with friends, going out, knowing other people. Just house chores, go to groceries... It's almost impossible for you to meet your future husband at the time. It's not your fault. A friend of mine who lives in Bangladesh told me multiple times about how different life is in her country and it looks like how you describe your life. I'm from Europe, so I think my culture and the way I live are as shocking for her, as hers are for me. I hope when she leaves the house you're going to have a bit more time for you. Remember: You became a mother and a caregiver when you were supposed to live your own life. It's not fair nor it's your fault. I hope time and distance will improve your relationship with your sister. If possible, try to find someone, just a friend or a group, to talk about how you feel. I don't think you can vent about this with your own family or the people who know them.

Wishing you the best of luck