So now I have three questions:
1. Can the identity of the Russian Colony of Montividiu be determined?
2. How many different types of Old Believer groups are there?
3. Where can I find more about the in-communion Yedinovertsy?
The Russian was largely meaningless fluff and didn't provide any good information at all. We'd need a speaker of Brazilian Portuguese to get anything useful.
1. I'm almost completely certain that they are Chapelists. They make the sign of the cross in the usual manner, if a little flamboyantly, and while the lestovka was absent in the video, that doesn't necessarily work against my conclusion. Likewise, their clothing was fairly consistent with what a Chapelist might wear, a specific example being the headdress worn by the married women.
While clearly some sort of references are made to the Russian Orthodox Church, there doesn't seem to be any indication that they are in anyway connected today.
2. Irish Hermit has a great resource here which I go through every few months. It's the best answer to your question that I've ever come upon.
3. My knowledge about Yedinovertsy specifically is almost nil so I'm not much help there.
With dictionaries not too far out of reach, I can read (after a fashion) some Russian and some Portuguese, but can only understand a bit of the former and none of the latter in speech. What little I got of the Russian was essentially what Hawkeye said.
As to your third question, I'd suggest a Google search using the terms Yedinovertsy, Yedinoverie, Edinovertsy, and Edinoverie. You'll get a 1,000+ hits, but a lot - probably most - will be brief mentions in the course of a discussion about Old Ritualists/Old Believers. There isn't a lot of literature from what I know. The movement wasn't and isn't strong from anything I've ever read. It never attracted the numbers that the MP expected - and then it lost at least one substantial congregation (about 1,000 faithful, IIRC) to the Russian Greek-Catholic Church in the early years after the Bolshevik Revolution. I've no notion what its numbers are at present and if the MP documents them anywhere on its site, I've not spotted it.
I appreciate Hawkeye's kind words about that collection of my posts to which he linked - though he credited them to my dear friend, Father Ambrose/Irish Hermit (that isn't the first time we've been confused for one another, but no one seeing the 7 smiling faces looking down from my mantle is likely to mistake me for a hermit/hieromonk
). The listings there - which are by no means complete - show the incredible numbers into which the Bezpopovotsi are divided. One can newly open most any text or monograph on the subject and discover an Accord that one had not heard of previously - and with varying degrees of detail available on what they believed, how they served, etc. Right now, I think I have a half-dozen about whom I know absolutely nothing except the group's common name.
It seems that within modern Orthodoxy (post enlightenment) the proliferation of such a variety of sects is somewhat unique to Russia. Does anyone have any insight as to why?
The following comments continue my remarks from above the quote immediately above and also address, at least to some extent, the question raised by David. Keep in mind that a lot of the divisions weren't a result of theological disagreement. Much of those stemmed from the geographic barriers of the times, the primitive communication capabilities, the self-enforced isolation to hide from official wrath and persecution (and the counterpart isolation enforced as exile by that same officialdom), and the lack of any central, hierarchical-type organization for the vast majority of the sects.
So, two groups with essentially the same theological outlook would not infrequently be catalogued under different names (often the patronymic of its local leader or the toponymic of the place in which it was situated) - because the two never encountered one another. Others would be differently named by two authors writing about them (there was a fascination about the Old Believers/Old Ritualists that generated a lot of text by folks whom we would likely term religious sociologists today, as well as authors who loved nothing more than an outrageous anecdote or description to spice up the 'travelogues' that were so in vogue in the 18th century. Differences in praxis could also be a consequence of the same geographic dispersal - just as happened in the early years of our own Churches, Orthodox and Catholic.
Then too, many - probably most - of those I refer to as Irrational/Eccentric Sects, Radical Sects, and Extremist Sects engaged in excesses of praxis and/or held such bizarre beliefs that 'mainstream' Bezpopovotsi would likely have outright rejected any connection with them, although they might have originally been rooted therein. Certainly, I think that it's a stretch to consider a lot of those to really be Old Believers.