My question is, how do you knows what to believe?
Make sure your heart is open to the truth. By that I do not mean follow your heart. I mean, make sure your heart is for God's truth no matter where it leads (even if it is the narrow path).
The Bible often interprets itself, so the more you know about one thing there easier it is to learn about other things.
Study both sides with an open mind. Try to determine which makes more sense. Which is most consistent with all of scripture? What are the problem areas and how can those be resolved?
Also, realize which side has the burden of proof. If I tell you that milking cows is against the will of God, the burden is for me to prove it, not for you to contradict it.
Scripture tells us everything that we need to know to be approved by God. So if polygamy is a sin, it should say so in scripture. Does it? If so, where? Where do other poeple think that it does, and does it really say what they are saying that it says?
If you have a specific thing that is nagging you or you can not seem to understand, feel free to post a specific question here. We love to discuss the Bible and what it says.
Best wishes and God bless you and your family and welcome to the forum!