My father was adopted. I believe that I have located his mother. Her father is my GREAT GRANDMOTHER's first husband. I have tested 3 1st cousins once removed??(Female 1 cm=673 on 29seg/female 2 cm=644 on 32seg/male cm=461 on 20.) on that line. My GREAT GRANDMOTHER*'s 2nd husband, I tested 1 first cousin once removed? or half first cousin once removed? (Female cm=615 on 27seg)? How can I identify which one of these husbands is my great grandfather?
I can't directly answer your question based on the questions I asked in the comment on your question. However, I can still provide you some resources to help you out:
- Blaine Bettinger's Shared cM Project (with probabilities) allows you to plug in shared DNA amounts and see what the possible relationships are and how likely those relationships are.
- Read about Lauren McGuire's "Simplified Visual DNA Comparisons," shortly thereafter dubbed the McGuire Method.
- Leah Larkin, The DNA Geek, has a seven+ part series of blog posts called "Science the Heck Out of Your DNA" which discusses using multiple relationship hypotheses and relationship probabilities to help determine the most likely relationship.
- In "Science the Heck Out of Your DNA - Part 4," Ms. Larkin introduces Jonny Perl's Probability Test Tool.
And, always remember to back up your hypotheses with traditional genealogical methods and documentation.