Hi Amy,
Welcome to the group

I'm glad you've found us there is a lot of support, information and tools to be found here.
I, like you am here because of someone not diagnosed with BPD offically but the shoe fits. However it isn't really about labels is it? It's really about how to deal with behaviors. Several things you mention ring bells with me regarding your brother's behaviors.
But being his typical self, he has now changed his tune (always) and has decided my Mum has it. Then my Dad has it. Then I have it. Now his girlfriend has it. He has always blamed everyone else for his issues in life as it seems he can make no fault.
You have this absolutely correct, he is projecting his issues onto everyone else because it it too hard for him to face/handle. Recognizing this is good, when we can recognize it really isn't about us it makes it easier to take these types of things less personally. Not fun to deal with but also not about us and who we are.
More on Projection...
https://bpdfamily.com/message_board/index.php?topic=70931.0He gets in INTENSE rages that include saying anything he could to our family to hurt us.
Difficulty regulating emotions is also a behavior all of us here recognize. When he goes into a rage what do you do? How do you and your parents react?
He thinks Dad is amazing and Mum is evil most of the time and tried to play them against each other.
This sounds like black and white thinking or "splitting". Someone is all good and someone is all bad and the two can switch, the all good person can become the all bad person and vis versa.
https://bpdfamily.com/message_board/index.php?topic=62033.0https://bpdfamily.com/message_board/index.php?topic=94786.0 A few days ago he messaged Mum saying he was going to put a bullet in his head so we all rushed over to his house to talk him down.
Have you ever thought about calling 911 when he makes a suicide threat? After all none of you are professionals, how about getting the professionals involved?
It sounds like BPD is new to you. When I first discovered it I did a lot of reading and found that really helpful in terms of getting a good grounding in what BPD is and what I was dealing with (the person with BPD in my life is my Partner's ex-wife).
Some reading suggestions...
Stop Walking on Eggshells: Taking Your Life Back When Someone You Care About Has Borderline Personality Disorder by Randi Kreger
The Essential Family Guide to Borderline Personality Disorder: New Tools and Techniques to Stop Walking on Eggshells by Randi Kreger
Overcoming Borderline Personality Disorder: A Family Guide for Healing and Changeby Valerie Porr, M.A.
Take Care

Panda39