You are getting great advice here SG....please listen. You finally started to detach and you saw great results. Then you gave in a bit with helping her with the car.
She wants a life without you? Then let her have it. Tell your mother to stop answering when she calls or if she feels she has to, then your mother needs to have a ready excuse as to why she can NOT take the kids when they're being "too much".
She can be a bad wife....she can even leave the relationship. She can NOT be a bad mother and she can NOT walk away from them. The same goes for you. No matter what, you both need to do whatever it takes to lessen the impact on them no matter what your issues are with each other. This is going to take a toll no matter what, but being mature great parents will help.
