Just remember there's no law that says you have to come out to anyone. I am in an MFM poly-fi V, and we've chosen to mostly stay in the closet. We have one friend and two family members who know, people we can trust to not spread it around.
Every poly family is different, and everyone has a unique way of doing things that works for them.
To those you choose to tell, just keep it simple, and offer to answer any questions they may have.
I hope that some of this helps.
Love means never having to say, "Put down that meat cleaver!"