Basically, the answer to this question is that we acknowledge our shared history and origins, but do not in any way consider them to be part of us. It's not like with Orthodox, Conservative and Reform Jews. To the best of my knowledge, they all consider one another to be "equally Jewish," for lack of a better way of putting it. The only one of these "Mormon sects" that would be considered relatively "mainstream" by most people is the "Community of Christ," formerly known as the "Reorganized Church of Jesus Christ of Latter Day Saints." It's the largest of all the groups that have broken off from The Church of Jesus Christ of Latter-day Saints. Its members now number somewhere around 250,000, while we have just under 16 million members. We do try to maintain good relations with the Community of Christ, I think primarily because it's to the advantage of both us and them that we do. We share more history and each of us owns assets the other also has a historical interest in.
We honestly would probably just prefer that the "Fundamentalist Church of Jesus Christ of Latter-Day Saints" (FLDS) and other polygamous groups not be associated with us at all, and we bristle when they are referred to as "Mormons." I'm probably different from most Mormons in that I don't challenge their right to call themselves "Mormons," if that is, in fact, what they call themselves. I say this because I try very hard to not have a double-standard. A lot of Christians say that Mormons (i.e. LDS) aren't Christians and don't have the right to call themselves Christians. I figure that if we are going to insist that we can call ourselves by that label if that's what we believe ourselves to be, it's hardly fair of us to deny the FLDS the right to call themselves "Mormons" if that's what they believe themselves to be. The FLDS are the largest of the polygamous offshoots of the LDS Church and we are every bit as opposed to their practices of child-marriage, etc. as anybody else is. We hate it when people imply that we're all just one big group and that some of "us" practice polygamy while others don't. There are other smaller polygamous sects, but I don't know a great deal about them.
Does this help? Or at least get us started?