P, I think it's important for the two of you to tell the boys together. You do need to be on the same page on what you are going to tell them. It may be helpful to do some research on the Internet before telling them.
My W was very eager to tell my S at the beginning of my situation. We finally did tell him about 3 weeks after her target date. We finally agreed on date to tell him. My heart goes out to you, man. I felt awful on that day.