Full or half cousins?

[AnnieBard]

I’d be grateful for more knowledgable folks opinions on this relationship.

Two siblings, one male and one female, are known to share a father but it is not known if they shared a mother as there are no birth or baptism records for the son.
The granddaughter of the male sibling shares 8% of her DNA with the daughter of the female sibling … 524 cM unweighted across 23 segments, the longest segment being 83 cM (Ancestry test results)
Are they more likely to be half or full first cousins once removed?

If they shared two grandparents I can stop looking for the other mother!

[QueenoftheWest]

I'm not one of the DNA experts on here, but I can provide anecdotal evidence to support their being full first cousins once removed, as my father's own full first cousin once removed shares 471cM with him on Anc*, which is slightly less that in your case.

The shared cM tool is also useful for visualising relationships:
https://dnapainter.com/tools/sharedcmv4

In this case, it says that the chance of the relationship being 1C1R is ~89%, whilst the chance of it being half 1C1R is ~3% but "falls outside the bounds of the recorded cM range (99th percentile)."

Queenie 

[Ayashi]

I have absolutely no idea, but if you've got a suspected mother for one or both children, I would focus on her ancestry. If you can trace her family a few generations back, you may well start to hit matches on her side. If you have a known descendant from her side of the family, you can compare whether or not they match to both of your target siblings. If one of your pair starts making many connections and the other doesn't match any of them, you may get your answer there. The flaw is a man who married/had children with two women from the same family, but I'd think that was comparatively uncommon.

[Biggles50]

The Granddaughter is one generation removed from their DNA Cousin.

The Granddaughter’s Mother probably will share about 900cM with her daughters 524cM match and that certainly is in the first full Cousin range.

So yes, it looks like the Father had the two children by the same Mother.

[AnnieBard]

Thank you Biggles, that’s really helpful. And thank you to the others who responded to.