Hi jmw

Dealing with a BPD family member is often quite challenging but since your sister has been officially diagnosed, you at least know what you're dealing with. When it comes to BPD I have experienced that knowledge truly is power.
My parents are steadfastly involved in my siblings life, managing almost every aspect of her existence in order to keep her safe and functioning.
I recently invited my parents to spend 2 weeks at Christmas with my family (I have two children under the age of 3). They really wanted to come, but insisted that they could not travel without bringing my sister. They booked her a flight to join them without even consulting me, though they know we do not have a good relationship. I am deeply concerned about how things will go with her here, particularly because I don't want to expose my kids to her tendencies to fly into a rage or behave inappropriately.
I can definitely understand your concerns. I am also concerned about the fact that your parents booked your sister a flight without even consulting you. Have your parents ever done such a thing before? I of course understand that your parents might be worried about your sister, but since it's your house it seems that your parents might have some problems with respecting certain boundaries.
I am struggling to find a way to do one of the following things: 1) either come clean and tell my parents I don't want my sibling here (they will be furious and deeply hurt) or 2) manage the situation in a healthy way if my sibling does come.
You alone can make this decision but by the way your phrased your first option, I would say it's totally clear that you don't want your sister there. If you would decide to go for option 1 I'd suggest you also try make clear to your parents how you feel about them booking a flight for your sister without even consulting you. It might help for you to read some information about setting and defending boundaries:
BOUNDARIES: Upholding our values and independence BOUNDARIES: Examples of boundaries Though my sibling was very abusive toward me when we were children, I do not physically fear her as I have not been physically attacked by her in many years, and I believe that she won't repeat that behavior. If anyone has any experience with this type of scenario, I would appreciate hearing from you. Thanks!
It's good that your sister hasn't physically attacked you in many years. Did anything happen that caused her to stop being physically abusive? Is/was your sister in therapy? I would still advise you to be very cautious though considering your past experiences with her. Especially since you also have your kids to worry about now. Has your sister ever been around your kids before and if so, how did she treat them?