Hi Justsomebelgian
Welcome to our online community
Growing up with a BPD parent can be very challenging and I am sorry you had such a difficult childhood. Considering what you've been through, I understand your concerns for your sister.
Great that you're reconnecting with your dad again

In what ways has this also been heavy emotionally?
Whether you are NC or not, I think the most important thing when dealing with a BPD family-member is to firmly set and enforce/defend boundaries. Do you generally feel comfortable setting and enforcing/defending boundaries with your mother?
You also worry about your own possible BPD traits. Many children of BPD parents have found themselves struggling with certain BPD-like behaviors and traits in their adult lives. This however does not necessarily have to mean that you have BPD yourself. Often this can also be learned or copied behaviors, which through hard work can fortunately also be unlearned or at least better managed. You might find this thread helpful which deals with this exact same topic:
Recognizing and dealing with our own unhealthy behaviors and coping mechanismsTake care
The Board Parrot