How do I comfort my child in this situation?

We are getting ready to move out of my toxic verbally abusive moms house and to a different state(she wanted us to live here to help her since she is older now). 5 hours away. My 4 year old constantly says he doesn’t want a new house and leave grandma but I know it’s best for us. He loves her & she treats him well, but She has turned him against me as well. I feel super guilty and sad though, bc his dad is gone and this is his only close family member. i’ve tried to work with her so many years but she doesn’t care at all to treat me like a human, now she tries to use my child against me which I will not tolerate, he has started saying ugly things to me then will run to her when I try to correct it & tell him that is not nice, and she will threaten me.She threatens to contact my abusive ex husband if I even leave the house, She also recently made me lose my job by bringing drama. She doesn’t want me to work. I have a new job in the new state , this is a small town with nothing, no jobs and a horrible school, plus my brother the only non toxic family member lives there so we will be near him. I was suppose to move January but delayed it due to feeling guilty, next month I have to follow through. I have no village here anyway UPDATE: I tried to talk to my brother about this and he told me I need to stay here with our mom and help her, I told him he could come help her just as well, so I won’t be including him in our plans anymore