It makes a lot of sense to have these fears, and it is a really good thing that your mom is speaking with someone. You mentioned that you are trying to move out, and maybe you are worried what might happen within your family as long you would not be there to prevent things from escalating.

As someone who struggles with very similar circumstances, it is especially difficult to release the grasp on the worries that concern family. For your own well-being, you can really only focus on the things that you have control over—the meaning that we assign to thoughts. It can get a bit tiresome to hear this advice, as if mindfulness training is a cure-all, but it can at least be a useful tool in those moments of panic, especially to focus on observing your breathing.

It seems likely that the dynamic between your parents and your sister will change when this move happens, and perhaps this would be a better opportunity for your parents to impose stronger boundaries. I wonder if there will also be a chance for your mom and your sister to attend therapy together.

Even if it is not BPD, emotional dysregulation and poor impulse control tend to have better outcomes with DBT and CBT approaches to treatment. It might help for your family to learn more about what DBT does in cases of BPD, but this situation is not something that families are equipped to handle on their own because it requires a great deal of objectivity to disengage with that level of intensity.

I really feel for the situation that you are all going through, and it is clear how deeply you care about everyone’s well-being. I am so sorry that this is happening and that you have been suffering—you are not alone.