AITA?

My sister is hosting a birthday party for my nephew but AITA if I don’t attend with my two children? Her sons father has threatened me, told me he was going to kill me, & called me out my name on 4 different occasions with situations that had to do with my sister & one situation that happened this year all because her car got stolen from me. My sister & I actually didn’t talk for 3 years because she didn’t stick up for me or even tell him not to be disrespectful even though the situations NEVER called for disrespect nor his input. In attendance will also be my father who im no contact with currently and who only has two kids (me & my sister) but has only been a deadbeat to ME my whole life & I tried to build a bond with him early on this year but he was only using me for resources because he was about to get evicted. Last but not least my grandfather who only has 2 grandchildren (me & my sister) but has constantly called her his favorite grandchild throughout my childhood. He genuinely doesn’t like me and I never understood why like since I was a child. I extended the invite to him to come to my children’s party, he didn’t respond to me but he responded to my sister and showed up which I was a little excited for but didn’t stay for my children to blow out their candles and the vibe just was off per usual with him. So with all that being said I don’t think I want to go, just thinking about it feels uncomfortable, im going to be on defense the whole time, and I won’t have my car back until the week after so I wouldn’t be able to leave when I want to if I do feel uncomfortable. I want to celebrate my nephew 100% but AITA to opt out of the party & celebrate him at my house with cake, decorations, & presents?