As has been mentioned many times, your family story is very compelling and heartwarming. There is, obviously, a tremendous bond between you and your sons and between them. This has been forged by the way you have all four navigated life following a heartbreaking experience. You know that the relationship they have with you is exceptional in every way and has made it possible for them to individually explore their separate dreams. Just as you have in every decision concerning your family, you will do the right thing when the time is right. Have faith in that. They may know, they may not. But, my sense is that they have been raised to appreciate the differences in people and to not to judge that which does not warrant judgment. While the disclosure may be interesting, I suspect it will have zero impact on what is important - and that is their love for their father. You will probably have to deal with the topic of your relationship with their mother, which may be a simple as their wanting validation that their was love there. On the other hand, they saw that love and may have no doubts. Good luck in everything that is going on with you and your sons; and a hardy congratulations.