
Hello ljfrogg and welcome
First, let me say how sorry I am to hear about your mother's passing. This must be a difficult time for all of you.
So it sounds like you're at a real crossroads with your sister. I'm sure it must've been very upsetting to learn what she had been saying to your son. My mom has BPD and I feel I walk a thin line trying to explain her to my children and prepare them, to some extent, while also not wanting to scare or overwhelm them. All that plus the betrayal you must feel from your sister's actions. I can see why you're upset.
It's good that you reached out for support. I think you'll find many members here who can relate to your story. There are also some outstanding readings. Here's one you might find helpful right now:
The Five Stages of Discovery for Family MembersHow is your sister handling your mom's death? Do you think that her BPD behaviors escalated at all around that time?