I was raised in it, and my parents went to know your religion seminars way back when, and had/have a set of the journals of discourses. This is a printed record of the transcribed sermons from Joseph Smith and Brigham Young....and other early church presidents. They believe that the modern current prophet speaks for God, even if he changes or (appears to) contradicts what previous prophets said or taught. What is called the manifesto was when the church agreed to no longer practice polygamy, to secure statehood for Utah. Many living "the principle" continued to live it, some down in Mexico to avoid persecution.
The lds believe they are earning a higher degree of exhaltation, which is why those in leadership in fundy groups desire multiple wives. This causes an imbalance in the world and all sorts of abuses happen.
I don't pretend to know that marriage continues beyond this life. All my reasons for wanting a sisterwife, have to do with love and support in raising a family in this life....another someone to build a life with that won't move away.
Lds lifestyle is pretty nice. They are family focused and clean living people. Many of my family are happy belonging there. We don't fight about religion, but I cannot claim the doctrine. It was very eye opening to attend a fast and testimony meeting after maybe ten years of marriage. The Sunday school lesson was about how all Mormon doctrine can be found in the Bible.....and I'll stop at saying, there is more then one way to understand what they claimed as proof texts.
Their "elders" are not biblically qualified. They are young unmarried men that are usually just referring people to tracts, videos, teaching aids and pre prepared answers.
*shrugs*
I'm going to stop now.