It sounds like you care very much about your sister and your family. It is difficult to deal with the effects of such a traumatic background, particularly when it's still affecting everyone even after the direct family dysfunction is no longer as present.
It seems you have taken a lot of the trauma on to yourself with this situation. Your sister's response to the childhood problems has spilled over into your relationship with her and her inability to see her issues separate from you sounds poor to non existent.
Fortunately, you have a choice in how you want to respond to your sister's behavior. But, only you can decide what steps to take. You have some choices in how you want to approach your relationship with your sister and her family. You definitely do not need to accept any type of emotional abuse either directly or indirectly. Increasing your own self esteem would go a long way in helping you see what is your sister's issues and what are your own. Defining the boundaries in your relationship with your sister would also help.
How do I do this?
Here are some steps you can take to make this happen:
Most of all don't blame yourself for your sister's issues. Put yourself first for a while. It may feel like you are going against your nature, but taking time to evaluate your situation and protecting yourself from further abuse is a critical step to success.
The above steps also apply to your situation with men and relationships overall. I think you will find that getting some perspective will go a long way towards solving this problem.
Hang in there and remember be good to yourself.
Optional Information: Gender: FemaleAge: 51Already Tried: Counselling with Accord, Catholic agency in my parish. I think she has psychotic tendencies and the constantly startled look in her eyes was noticed by my former fiance.