I agree with other posters, and I think this sudden change is probably already upsetting your children so I think it's important to make sure that you don't do anything that could lead to your son being traumatized. After all, he knows you as his father, it could devastate him if he were to find out he is not your biological son. Fourteen/Fifteen is still such a young age and he will not have the ability to handle this or even that it matters to you on some level.