It is hard to talk about these things with others, so congratulations on making the first step by posting here. You are welcome here any time. Also, your feelings, thoughts and emotions are most certainly, 100% valid!
If I could give some advice, I would say that you should look after your own well-being and the well-being of your family first, but if you can communicate to your sisters and their families how they have treated you and how they made you feel, they may understand.
Just to add on to what Sophie_M has said, and if you are feeling like you need someone to talk to about anything, you can also contact Beyond Blue Support Service on 1300 22 4636 or on Webchat 3pm-12am AEST at www.beyondblue.org.au/getsupport . There is also Lifeline on 13 11 14 or the Lifeline crisis chat 7pm - 12am at https://www.lifeline.org.au/crisis-chat/ .