Okay I should I continue to help my mom out who has cancer but she is so critical of me and then we argue?

She is in stage 4. We never got along, but I try to suck it up and help her out with groceries etc and cleaning the house for the past 5 years. My autistic brother lives with her. Recently he threatened physical violence (he was NEVER violent towards me in all the years I've known him...and screamed at me "I HATE YOU!!!!"...my skinny, boney, cancer-ridden mother was the one that got between us and prevented him from starting to hit me) because we got in an argument (and my mom was mad at me too because I was rubbing her the wrong way...I guess cuz I was so beat and tired from grocery shopping, carrying all the groceries, and then driving 1 hour to the house), and now I'm scared to go over and help her. It really rattled me. I'm sure if we had a gun in the house, I'd be just another statistic.. He is really a good guy, but I guess the stress of the situation is getting to all of us. She was diagnosed with stage 4 cancer 5 years ago and is still surviving. It gets harder every year though, as she's not getting any younger and she can die any day...the chances grow as the years p of course. When she dies, I always thought I could let my brother live with me. But I have never seen that side of him before. I feel like if I have a husband, he will be SUPER MAD if my autistic brother ever threatens me. So now I'm rattled, worried, and don't know what to do. Please any advice would help (even a prayer) thanks.