Why does my step-uncle hates my mom and I?

My mother’s boyfriend started to date when she was 30 and he was 25. He raised me like his daughter cause I was only 5 when they met, and we are extremely happy together, but everytime his brother come to visit us, he start calling him a “ beta” or a cuck. He did it when I was 18 and he was 38 by telling him that he should be dating me instead of dating my mom, he called me a mistake when I was 10 when we were alone by telling me that my mom and I are ruining his brother’s life cause he deserve a way better than a single mom, since he’s successful. He also posted a weird video on his Facebook page about some dating coachs saying how dating a single mom is awful and a looser move , ( it was definitely aimed toward us).

My step-dad usually ask him to shut up and to mind his own business , and I wanna stand up to my self too now that I’m 19 but my mom told me, to stop never do it, and that replying to that kind of human is giving him the attention he doesn’t deserve. we tried to be nice with him, but he keep annoying us and disrespecting us!

That’s the thumbnail of the video he posted by the way:
Why does my step-uncle hates my mom and I?
Why does my step-uncle hates my mom and I?
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