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After discovering my grandfather wasn't related (my DNA showed zero relative matches on all sites for this man) I had my 3 brothers, a sister, my niece, and 2 of my children (who are half-siblings) tested. My father passed years ago. DNA matches narrowed down to 2 long-deceased brothers. One brother's 2 daughters and many of their children and grandchildren have tested & match me and my sibs etc. closely. Example: Female 86 shares 1321cm with my brother & between 815-925cm with the rest of us. Her sister 80 shares 580-910 with us. 86 F's daughter shares 350-525cm with me & sibs, 80 F's daughter shares 350-518cm. Other brother had no children, no way to compare. However, he lived in the same apartment building in downtown Indianapolis in 1931 as my grandparents. Our Dad born in 1931. Brother of all tested descendants lived close to Indianapolis.

Is there a next step we can take to prove which brother is our grandfather?

Should have added that I uploaded all DNA tests from my family and a cousin's test from the other family to MyHeritage & trying to use their tools. Also subscribed to DNA painter and trying their tools but confused by WATO. In all, I have complete subscriptions to Ancestry, MyHeritage, 23andme, DNA Painter and FamilySearch

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WATO at DNA Painter is designed to help with situations like this. I just used it as follows (note I don't have all the info and may have misinterpreted):

  • I built out the tree with the two brothers and the descendants of the brother with the descendants you mention
  • Next you would need to add the cM amounts that someone in the oldest tested generation shares with them (if I understand correctly, this would be you or your brother). I added the 1321cM your brother shares.
  • I hovered over each brother in turn and clicked 'add child' to add a node representing your father.
  • I hovered over the node that's a sibling to the 86 and 80-year old females and clicked 'define half relationships'. I checked the box next to both females to indicate that they would be half-siblings to your father if he is in that position.
  • The amounts you share with these females' daughters are not relevant since their mothers have tested.

The result seems conclusive in that it suggests that the brother who is the father of the 86-year old female with whom your brother shares 1321cM was your father's biological father. Here is the link: https://dnapainter.com/tools/probability/view/866b5b8c62a7f3f4

To repeat: I've only added one match, but unless I've misunderstood:

  • If Brother 1 (father of the 86 and 80 year old females) was your father's biological father, then the relationship the sisters would have with your brother is half-aunt/half nephew. 1321cM is high, but in range for this relationship, as are the 815-925cM figures you mention
  • If Brother 2 (no known descendants) was your father's biological father, then the relationship the sisters would have with your brother is 1st cousin once removed. 1321cM is far too much DNA for this relationship, so in order for this to be correct, there would need to be a secondary relationship that's also contributing DNA.

Based on the info you've provided, it seems most likely that 'Brother 1' in the image was your father's biological father.

screenshot of the WATO tree showing how the half-aunt/half nephew relationship is feasible for Brother 1 based on the amount of DNA your brother shares with her screenshot of the WATO tree showing how the 1C1R relationship rules out Brother 2, unless there is a secondary relationship

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  • So the fact that my brother shares more DNA with these relatives than the rest of us is just the way it happens sometimes.......yet that very fact is what makes this relationship conclusive, right? And me and my other 2 brothers and sister do share at the high end of possible relationships is what I've seen from your tools. Just shared this info with my cousin, who's the daughter of my newly designated half-aunt!
    – Kdaline
    Jul 8, 2023 at 23:51

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