Being blackmailed by your father through your brother

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Hey guys, so I have a father who's a dick. My parents separated when I was 3, I visited him regularly throughout my childhood. The relationship was always complicated but to keep it short, he's a narcissist with borderline syndrome + an asshole in a lot of ways. So that's him. He had another son after me who is now 8 yo, I am 22.
My father caused pretty elaborate psychological problems on my side, which is why I quit contact with him several times throughout my youth. After becoming clinically depressed 3 years ago and realizing it was due to him being somewhat in my life I put the contact on hold to get better and into a state where I care to live again. In these 3 years I have been in therapist non stop and in a special clinic for treatment for 9 weeks. So my father has had a very bad influence on my life but I'm recovering. He's close to being the worst dad you can imagine without being physically abusive...
Now that I recently told him I still need time and will continue to keep the contact on hold he has started pressuring and essentially blackmailing me with my brother. He tells me my brother misses me a lot and it hurts him that I am not in his life. And that it is damaging my brother that I won't get in touch. Therefore if I don't get back in touch he will tell my brother that I am "gone".
I know that getting in touch with my father again will be my downfall. I can't handle it and it's essentially not an option. I love my brother and I fear I will lose him forever if my father tells him some bullshit about what happened to me and why I left his life.

I guess there's no clear question here but what do? How do I deal with this? Should I just give up on my brother completely and never talk to my father again?