Records show that both Joseph Smith and Brigham Young were 'sealed' to multiple women in their lifetimes. To be 'sealed' means that you will be linked with that person in the afterlife, and does not necessarily pertain to relationships in this life.
It is not evident that Joseph Smith ever had a romantic relationship with any of the women to whom he was sealed. DNA testing has not been able to prove any children born to these women were his, nor are there any journals or records of him having any type of marriage relationship with them.
Brigham Young did have a marriage relationship with about half of the women to whom he was sealed and bore children through many of them. For several others, being 'sealed' meant that Brigham would provide financial assistance but not consider them 'wives' - as there was no welfare program in place at the time, this was one way to care for widows. Others were 'sealed' to him for 'eternity only' but remained with other (usually non-Mormon) husbands during their lifetime.
Mormons believe that in order to attain the highest levels of heaven, one must be 'sealed' to a member of the opposite gender in a Temple ceremony. In the early days of the Church, it was quite common for a woman who was unmarried or who was married to a non-Mormon to be 'sealed' to a faithful Mormon man. Sometimes that was the only time they would ever see each other. It did not necessarily mean that this couple was 'married' or ever had a romantic relationship. Now, only legally married couples may be 'sealed' together.
Brigham Young actually didn't make many changes to the Church. Everything that Brigham Young did was in response to previous instruction given by Joseph Smith. For example, Brigham Young moved the Church to Utah because Joseph Smith prophesied in 1842 that the saints would find peace in the Rocky Mountains. Brigham Young expanded the practice of polygamy, but Joseph Smith had preached in favor of the practice as early as 1831 (polygamy officially began in 1843, still with Joseph Smith's approval). Brigham Young also expanded the practice of consecration (the 'United Order'), which Joseph Smith taught in 1834. (The practice is also found in the Bible and the Book of Mormon.) Brigham Young also expanded temple building (begun by Joseph Smith) and performed temple ordinances, which were given to him by Joseph in 1842.
Probably Joseph Smith, since he restored the church and was the one who lead them across the plains to the Salt Lake Valley.
yes
Mormons
Joseph Smith and Brigham Young
Joseph Smith.
No. Brigham Young was in the eastern states.
Brigham Young's last words were "Joseph, Joseph, Joseph" presumably about the Prophet Joseph Smith, Jr.
Brigham Young practiced polygamy because he believed that God had commanded him to do so.
Members of the Church of Jesus Christ of Latter-day Saints (the "Mormon" church) believe that Joseph Smith's successor was Brigham Young. However, many offshoot groups claim other successors, such as Joseph Smith's son, Joseph Smith III.
Brigham Young.
Joseph Smith was the founder, and he was in upstate New York at the time. Brigham Young took over after Smith's death.