I’m very sorry to hear about your sister’s suicide attempt. It seems to me that the dynamics in the family are extremely intense, negative, and not conducive to your well-being. Because of this there are three options that I think make sense:
First, I would talk to your parents about the need for family therapy following your sister’s attempt. Often families need counseling to cope with the reaction. It was a traumatic event for everyone involved. I would look for a family therapist to assess where the family is at and offer guidance and perhaps some brief therapy to get the family going in the right direction.
Second, if this isn’t an option for you and your family I would look for alternatives to living at home. You state your age as 20 and it may be worth looking for a roommate you can share expenses with and find some room to breathe. While I realize the financial situation may be difficult, staying at home seems to be a much greater burden.
Finally, if neither of the first two options are viable I would suggest you plan for moving out. Having a plan, even though it may be a year or more in advance, will keep you motivated, focused, and perhaps a bit more able to cope.