BPD sibling threatening elderly parents with legal action

I need advice.

My BPD sibling is increasingly referencing lawsuits she plans to bring against my elderly parents. I do not believe this is made up - She even tried to sue the therapist who diagnosed her. She has a history of this kind of stuff.

Even the threats and intimidation are impacting my moms health. (She literally told me so after being in the hospital recently.)

What can/should I be doing to protect my parents?

Im NC for nearly a decade with good reason. But I have overheard or had them tell me several times she has referenced legal action against them.

Is there a type of attorney who can put protections in place against an unwell sibling with nefarious intentions?

As they are in their 80s so elderly - I really worry. Recently my sibling also tried to convince them to let her take over control of their affairs etc. She did not succeed but I worry the behavior is escalating.