Well, if you are going to be worried about judgments coming from a good portion of your guests, then you won't be enjoying your own party much at all.
So, since it's all new for you and you are still getting acclimated to the situation, maybe being brazenly, totally OUT might not be a great idea. Introduce them as your friends or just by name. If people want to know more, you can talk about how you met, say that you're really close, etc., and gauge which people would be okay with knowing you are seeing them both on a case-by-case basis. I don't think you need to get defensive with people ("I'm not a slut.") -- it's nobody's business, really, and you don't owe anyone an explanation.
When you do feel like there is someone you want to reveal more to, just do it nonchalantly like it's the simplest thing in the world. I mean, really, if you had two platonic friends visiting town, how would you introduce them?
Another thing to talk with your guys about beforehand is the level of public affection they would be willing to engage in. So ask them.
When you wrote: "I'm honest but awkward about explicitly acknowledging the situation because I'm so new..." did you mean revealing yoru poly life to people outside these relationships, or were you saying you feel uncomfortable talking to each guy about the "other one" and stuff like how to manage events and situations like this, whether they want to meet, how comfy they are with others knowing the depth of your relationships, PDAs, etc.?