Nobody is in a better position than you to decide what sort of effect your mother will have on your child. You must understand that your relatives from your mother’s side may only be trying to mend things between the two of you and you should try not to hold that against them. There is obviously a communication breakdown between your mother and you. The fact that on your son's second birthday you are reconsidering your decision to keep her away from him shows the ambivalence that you maybe feeling about your decision to keep her away from your own life as well. At this point you should listen to your own instincts and if possible try and mend your relationship with her first. I would suggest that you explain to her that her behaviour is not acceptable to you and that both of you should consider counselling immediately. Family therapy can be a good option and I also suggest that you see a psychologist anyway, to resolve and avoid any effect that the past may have on your present or future family or personal life.