i feel so guilty

my dad is having upcoming heart surgery and wants me (19 f) to care for my younger brothers both (m16). one of them has anger issues and the has autism that goes untreated because of my dad. I no longer can emotionally be around it and have been staying at a family members. I knew that i wouldn’t be able to handle it. and for once i placed some boundary and told my dad i can’t do it but i could help out in some aspects still. he blew up on me and told me never needed me to help anyway and that it doesn’t even matter to me that he’s having heart surgery. it does but god i’ve been so emotionally beat down these last few months, and this surgery is happening at the same time as all my school finals. i feel guilty for doing this but a part of me feels good about it. i can’t do it, and i know i cant. it wouldn’t be fair to me or my brothers to be around one another in such stressful times because none of us know how to cope. i feel like im just running from all my problems but i dont know. pls help