What is an unambiguous way to describe the resulting relationships when a widower with a child marries his deceased wife's sister and has children with her?

Not the stepmother-aunt stuff for the first child, but how can the relationship between the first child and their sibling-cousins (and subsequent generations) be described?

Family A: Father 1 & Sister 1 (dies);leaving Father 1 remaining w/Child 1

  • Child 1

Family B: Father 2 (dies) & Sister 2*;leaving Sister 2 remaining w/Child 2*

  • Child 2

Family C: Father 1 & Sister 2; inheriting Child 1 & Child 2 and having Child 3 together.

  • Child 1 (From Family A)
  • Child 2 (From Family B)
  • Child 3 (From Family C)

Child 1 & Child 2 were originally 1st cousins, but now what they are is not as clear to describe their dual relationship.

What are unambiguous ways of referring to child 1's relation to 2 & 3, and 2's to 1 & 3, and 3's to 1&2 in the new family C group?

  • Welcome Hengest to Genealogy & Family History; please be sure to take the tour and review the help center section as well. While [this is a slightly different question][1] than this one, I would still check it out for reference. [1]:genealogy.stackexchange.com/questions/9253/…
    – CRSouser
    Commented May 20, 2016 at 17:25
  • I also edited your question to have an outline view to illustrate your question a bit and expand on it as well as it wasn't clear if you were just talking about child 3 or child 1, 2, and 3's relationship in the original question. I've had this scenario in my tree as well so am curious as well.
    – CRSouser
    Commented May 20, 2016 at 17:38
  • Didn't you mean Father 2 and Sister 2 for family C ? How could Father 1 revie ? Or did he get illegitimate children with Sister 2 before dying ?
    – Bregalad
    Commented May 20, 2016 at 19:01
  • Have you tried following the advice at genealogy.stackexchange.com/q/6818/19 ? In particular, the Relationship Calculator of Stephen P. Morse
    – PolyGeo
    Commented May 20, 2016 at 20:32
  • @Bregalad No Father 1 as he was the widower left over from Family A as the women dies in Family A and the man dies in Family B; family C is made up of the combined left overs plus a new offspring. I was the one who added the table so clarified with explanation so hopefully that makes more sense to you.
    – CRSouser
    Commented May 20, 2016 at 22:35

1 Answer 1


I think that:

  • child 1's relation to:
    • 2 is 1st cousin
    • 3 is 3/4 sibling
  • child 2's relation to:
    • 1 is 1st cousin
    • 3 is 3/4 sibling
  • child 3's relation to:
    • 2 and 3 is 3/4 sibling

According to Wikipedia:

Three-quarter siblings have one common parent, while their unshared parents have a mean consanguinity of 50%. This means the unshared parents are either siblings or parent and child (similar terminology is used in horse breeding, where it occurs more frequently). Three-quarter siblings share more genes than half siblings, but fewer than full siblings.

There is also a term of sibling cousins listed in Wikipedia:

"Sibling cousins" are those who have the same mother with their fathers being brothers or cousins or who share the same father with their mothers being sisters or cousins. This is a broader category than, but inclusive of, the 3/4 sibling above.

but I think the terms 1st cousin and 3/4 sibling are more useful in the situation you describe.

  • Three-quarter siblings and sibling cousins are interesting concepts but I think the point is that 99% of general readers won't have the faintest idea what is meant by the terms. If the reader doesn't understand, then it is hard to argue that the term is "unambiguous". Far better to simply describe the exact scenario - that X married his deceased wife's sister (perhaps in defiance of requirements) and there were children from both marriages. End of?
    – AdrianB38
    Commented May 23, 2016 at 14:25

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