Narrow minded Christians are just going to condemn anything other than one man one woman marriage. So, same sex marriage and secular arrangements like having more than one lover are just never going to be acceptable. More liberal Christians, you might have a chance, if you just go with the God is Love concept.
There comes a time when you're going to have to go your own way, whether it's around this, or other things like parenting, clothing, music, food, gender identity or preference, travel, hobbies, or whatever. You might remain a Christian and explain poly to yourselves to your own comfort, but it may not work with your parents' kind of Christianity. You can't live your life to please your parents. I mean, you can. But who would want to?
It can be hard to "come out." And you will be condemned. Most parental units will come around after a year or two. But the really conservative ones just never will. So, you either stay closeted, and live in fear they will find out somehow, while you're lying and sneaking, or you come out and be proud and let the chips fall where they may. If you lose blood family, then they weren't worthy of you anyway. And then you go make a chosen family of people who get you, that you don't have to hide your true self from. And you find your bliss.