As an SO, even though I have been on board with my fiance's journey from the beginning, going to therapy sessions with Tara was really helpful for me to get a better idea of what was going on in her head, and what she was worried about. We've done fairly well with communication all the way through so far, but it really helps to have someone in the room who knows the right questions to ask.
If I were in your position, I would probably hold off on telling your wife that you are definitely going through with the full transition, but have another conversation now about how your current lifestyle is making you feel. If she does get mad when you later tell her that you have decided on the full transition, explain to her that you couldn't deal with the rejection that you were expecting on top of everything else at that time, and that you were trying to prepare her more for the news before telling her. It might not help much, but I expect that it will help. The biggest thing is not to lie to her. If she guesses that you are going through with the transition, you will have to tell her.
What about your sons? It seems to me that they could be your allies. I am guessing that, since only one of them is going on vacation with you, that they are older? If they are, you should make sure that you have this conversation with them as well. Really, even if they are young. If they know that you are making an effort to be open and honest with them, chances are they will feel kindly toward you.
I hope things work out for you!
-Owl