Hey yamada: I read a few of your prior posts. If I understood correctly, both your mom and sister have BPD. Is that right? Is your sister still living in a different state?
How do the stories differ about the need for money? What do you believe your sister really wants the money for? Do you think your sister is trying to take advantage of your parents?
It might be helpful to read about various types of triangulation.
https://bpdfamily.com/content/karpman-drama-triangle