Havehadenuf,
I'd like to welcome you to bpdfamily, I'm sorry to hear that you're going through a difficult time. It sounds like your dad probably has boundaries if your brother is trying sway him by going through you. I wouldn't pick sides because you, your dad and your brother make a triangle.
We're just going to use a pwBPD for an example, a pwBPD will rarely cast themselves as persecutor, usually they'll cast themselves as victim or rescuer, BPD is a persecution complex where the person truly believes that their circumstances are caused by others and not by their choices or actions. In your situation, if you'd do as your brother asked, you'd cast yourself as rescuer because your father is cast as persecutor for not giving into the demands of your brother, to stop the drama, you have to remove yourself from this dynamic, be objectionable and not biased by picking a side.
Escaping Conflict and the Karpman Drama TriangleI'd suggest to self protect because of how it's affecting you, I'm not suggesting to do it permanently, you could do it temporarily until you feel like you're recharged.