I have been trying to figure out that one myself: similar situation, where there's a pedigree collapse due to two siblings ([[Richardson-18778|Barnett Richardson (1760-abt.1840)]]) marrying another set of siblings ([[Martin-12613|Nancy (Martin) Richardson (abt.1776-)]] [[Martin-12611|Elizabeth Betsy (Martin) Richardson (1772-1832)]]) and it goes on and on because not only do I descend from the above mentioned group, I also descend from a third Martin/Richardson union, as well as the Teels who are also connected to this family, etc., which makes things look crazy on the DNA side of things, and I'm talking like 123 matches whoa for these connections, AND because this ISN'T my main paternal Y-DNA "Martin" line, it would appear that a lot of the matches are assumed to be in this line creating an "overcast" in comparison to all my other matches. so the good news is that I know I definitely descend from this family* but trying to triangulate matches, I have found a few keys:
1. You have to keep all your lines in mind. That is to say it isn't enough to have a match on a certain segment on a certain chromosome, but also to be able to make sure it's the "correct" chromosome you have triangulated, and I do that by triangulating my closest known matches so if it's my paternal line, I compare the match with my father to make sure it matches him as well, and also with my mother, to make sure it DOESN'T match her on that same chromosome.
2. The closest, shortest pathway is the one to use, that is confirmed: that is to say kind of ignore the ones where you have found multiple pathways, and/or in the process of adding their tree to yours, it's probably the shortest most direct pathway, as in you can start to see that the MRCA is just that, regardless of multiple connections to and around those people; in fact, because of this, you likely have "more" DNA from this couple as a result, and "more" cousins, too. They don't all match exactly where you want them to, however: at this point you need to consider the "rules" of endogamous DNA which can look very similar due to the overlaps in connections, but are not as "accurate" in cM/relationship as other families tend to be due to this. So, as a result, you may think you are looking at a close cousin who is in reality further away in the tree than another cousin in this family group that was the known child of your great grand aunt or whatever, and in this case this person is the one to anchor the DNA relationship, and not the more "overlapped" cousin... this is to say why triangulation is so important. You may discover the MRCA is a generation further back than the results would guess, or where they are expected to be in the tree, but with "way too high" of shared DNA to be "there"...
3. If you can say with relative certainty where 3 people match on a chromosome segment, then that is the person to build from, checking how the other matches in the family not only compare to you, but also your certain relationship with them, repeating the process, and that is to say kind of ignoring the "extra" DNA and "overlap" and getting right to the MRCA and triangulating that with certainty, making note of the earlier MRCA "double ancestor" attributing to the additional "boost" of that DNA lineage.
So for example, I have a lot of overlap in the Richardson/Martin family, and as a result, the Martin/Caffery lines... I see that I have a ton of matches, but only a handful have been proven to be super easy for me to find our MRCA despite the overlap, and as a result have been key matches when looking at unknown ones, but certainly descending from this same very large family.
I hope this will help you and others, and myself too: I think it's really cool that we attempting to master such new technology and science and making meaning out of it. It's difficult, but not impossible and I love this community you all are very motivating in my own research!!