So it looks like I'll be competing against 3 people for the promotion in my own damn job. What will I do about this?

Deciding that I had better prepare myself for disappointment and decide what I am going to do to overcome it. I've done it before, I can do it again. It's not what I want to do, but sometimes life doesn't go the way you hoped and it's better to get up and do something about it rather than lay down and sob over it. I refuse to be a victim, I will use everything that happens as an opportunity to find the better option hiding somewhere else.

In other words, if they give it so someone else, I'm finding somewhere else to work hard.