Welcome Anonymous99: I'm sorry about the situation with your sister and family. It sounds very frustrating.
She lost job after job and went through serial boyfriends, addiction shoes and drinking.
Is the reference to "shoes" a typo? You say she has a drinking problem. Is the other addiction to "shoes", as in perhaps excessively purchasing shoes?
My Dad has been trying to save her and has now decided that my sister is too fragile to stay on her own (she is not) so my parents won't leave her alone in order to visit my kids... .their only grandchildren.
What are the behaviors your sister exhibits that you think lead your dad to believe your sister is too fragile to stay on her own? Is your sister getting any treatment, meds or therapy?
How can I get my parents to understand my perspective be there for my children without my BPD sister tagging along for every visit, vacation and event?
Unfortunately you can't change either your sister or father. You have set a boundary for the safety of your children and that is understandable and prudent. All you can do is let your parents know how much you want them to be a part of their grandchildren's life (without your sister, in her current condition). You can't change your dad or your sister. All you have power over is your boundaries and how you interact with your family and react to your family.
Have your parents tried some therapy, in order to gain a common strategy for them to use in regard to your sister? If your sister refuses to get treatment, and your father continues to enable her, there isn't much you can do.