I know all that was very confusing. I've probably used some possessive pronouns without clarity, as in "their children."
To clarify: I was not talking about an ancient Egyptian or Incan royal marriage - no brother and sister wedding each other. The closest marriage I ever saw between Catholics in Ireland was 2nd cousins. Most consanguineous dispensations that I've seen were not even for 2nd cousins, but either for 3rd cousins or 2nd-once-removed. The Irish were not an inbred lot, at least not in the 1800s.
Sinann, that is an interesting point about the "nephew." Ruskie, good point about names.
I am descended from John Brien, (m1808, my GGG grandfather) and know that I'm related to someone descended from Julia Brien (m1820, other's GGG grandmother). It seems certain that they were related somehow. I am not descended from either 1911 household (headed by their respective grandsons). One head (c1911) was the brother of my G grandmother (b1870), so the wives of the heads on the census don't obviously enter into it.
I'm sorry, I know this is all very confusing, I'd give more names, but I'd hasten to add there is no direct connection. I'm interested in the idea that John and Julia were brother and sister, as Julia (m1820) may have a surviving baptism record from 1799. If they were siblings, it follows that Julia's parents would be John's parents, ie. I've found my GGGG grandparents. But John was older than the surviving record (only goes back to very late 1798), and he certainly has no surviving birth record, ie. John and Julia cannot be directly connected through their earlier ancestors.
The only evidence is circumstantial evidence, and it is kind of a weird parish. There are different gaps, some small and some large. The heads on the 1911 census were born in a large gap, they and their siblings have no surviving baptism records. One even has no birth record, but I'm still able to trace it back to John (m1808) and Julia (m1820), their respective grandparents, with virtual certainty.
I have found various bits of circumstantial evidence - it is a very complicated theory. But I'm sure nobody is interested in bits of very circumstantial evidence or very lateral names. Suffice it to say, John (m1808) is inferred to be tied to the 1799 townland and, his unknown relation, Julia is inferred to be Julia (b1799).
I hasten to repeat there are no direct connections. I've searched very thoroughly and am quite certain. What I'm interested in is purely an abstraction, based on "relative" on the 1911 census and the reasonable theory that John (m1808) and Julia (m1820) were related:
If we accept that John (m1808) and Julia (m1820) were blood relations and we accept that their respective grandsons (heads, c1911) were related by blood through them, and had no equal or closer blood relationship along a different line, then to what degree where the heads (c1911) related, based on the child of one being called a "relative" in the others household?
I am sure of all the incidentals. I know we cannot be sure of the conclusions, but I'm interested in impressions - that is what I am soliciting. Were John (m1808) and Julia (m1820) more likely to be siblings (ie. I've found my GGG grandfather's parents) than first cousins?
In other words, would someone leave their 3 y.o. child with 3rd cousins? Or put another way, would someone, with several young children, take in their 3rd cousin's 3 y.o.? When the widower had obvious siblings closer (though crowded living)? As Julia (m1820) had many children, presumably the widower (c1911) had many first cousins, but more distant (6-8 miles). Would the heads being 2nd cousins (ie. John and Julia were siblings) be a lot more probable than the heads being 3rd cousins (ie. John and Julia were first cousins)?
Or if that is all too complicated, I'll just put it another way: what is the most distant blood relationship you have ever been able to work out for a "relative" on the census? Preferably a child. And assuming an actual blood relationship, not something by marriage or godparent. I know Irish records are messed up, so I'll take any European country or offshoot like the US or Canada, as well as Ireland.