My brother (M27) does not respect my decision to disown my mom (F67)

Hello i am a young guy(M25). After reading Stefan Molyneuxs philosophy(Real-Time-Relationships, On Thruth: The tyranny of illusion) i finally understood the logic of love. I therefore deFOOed (disowned) my leftwing mother(F67). She also did not stood up for me when i was bullied and evdn forced me to go to school. I am still in contact with my brother because his views do more align with mine. I do however don't agree with how he sees leftwing people. I told him i made my decision and the relationship is over. He tries to get me in a mediation with my mother, him and a social worker. I told him i don't want to be attacked by 3 sides and that the relationships is not going to change unless my mother changes her mind.

The other day i was visiting him and his roommates were also present. In the presence of his roommates he said i have to talk to my mom. He also said twice i had to phone my mom and ask how it is going with her. Stefan Molyneux said you need to force your other family members to also take sides to not allow things like this to happen. I kinda think i am stupid for not doing that but then i also love my brother and don't want to lose him. My brother clearly does not respect my decision and thinks things can be fixed. I am losing patience with his behavoir. How can i get the message across that i am done with his behavoir without setting a ultimatum?

TL;DR: My brother (M27) does not respect my decision to disown my mom(F67). He asked me to call my mom two times and is pressuring me. How do iget the message across that i am done with his behavoir without setting a ultimatum?