I'm going to threaten to never let my mom see her grandkids
Are you really serious? Why would you threaten your mom with this?
I'm done with my mom and she doesn't deserve to see the grandkids
Threatening your parents to withhold their visitation right with their grandkids will further escalate any issues you have with them. Sometimes bad parent's can make good grandparents. You should air your grievances with them and talk out your issues before taking any drastic action.
They threaten me and makes my life hell, why can't I do the same?
You really should discuss this with your parents and let them know how upset you are before taking the grandkids out of the equation. See what they have to say first.