You're going to have to learn to ignore the awkwardness. If you let something as inconsequential as that stop you from speaking your thoughts to those closest to you, you can expect to have a long life of frustration ahead of you.
You're going to have to ask them. Ask them if they know any poly people. Ask them what they think about it. Ask them if they've considered trying it themselves.
And if they want to know why you're asking, you're going to have to stand brave and voice your thoughts, speak your truth about what you're interested in. That's how you're going to get the relationships you want to have--by speaking up about what you want and finding people who are interested in the same sort of thing.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.