Hi and Welcome,
UtterlyConfused! 
I'm so sorry to hear of the troubles you're having but I'm glad you found us and are reaching out for support.
You'll find many other members here who are going through similar struggles, we are learning together how to enjoy more peaceful lives, there is hope.
I'm a grandma as well and I know how heartbreaking it is when my GS4 (4 year old grandson) is used against me, it's just awful.
I recommend that you read and learn all you can about BPD and we can definitely help there - we've lots and lots of articles and workshops. A good place to start is the thread pinned to the top of this board,
HOW TO GET THE MOST OUT OF THIS SITEThe best thing about bpdfamily is the supportive community filled with lots of others who are learning. Post here, read and join other's threads, you will begin to build a support network, so critical when navigating these intense relationships.
What are the behaviors that led you to suspect BPD?
I'm glad you've joined us,
UtterlyConfused ~ OH