Why would my sons wife sever our bond and relationship with their 4 children..?

I read your whole post. It's really hard for me to make a judgment call on this because I don't know you or anyone else in your family personally. I can say for sure that I'm very sorry this happened. I think it will work itself out. I am not a mother-in-law, but I have one, and I can say from a daughter-in-law point of view that she might find you to be overstepping your bounds sometimes, a little bit smothering, and highly annoying. It kind of comes with the territory of being married. I also feel that loving, involved grandparents are extremely important to children, and I hope that she sets aside her own personal feelings and perceptions and does what is best for her children, which is to step aside, allow you to enrich the lives of the children, and keep peace in the family. I wish you the very best.