That bitterness you carry obviously caused you the marriage. I am happy that you saved the man loads of troubles by divorcing or accepting divorce. You said age is catching up and you may never have another child? You seem like no man will want to have a child with you even by accident..
Why bother changing children's names? Clever woman, for example, Wangari died while still using Maathai's name yet they divorced in the 1970s. Yet you want to go to the extent of even changing the childrens' names. For me, names do not matter but what will you tell them is the reason for changing names? That the man they call their father is not after all? Many women say such things after parting with the father of the children. Please do not punish the children psychologically..