I have recently learned that my father is not my biological father. Please see the Ancestry DNA screenshot.
The first person in red is listed as a first cousin but I know for a fact she is actually my aunt, my mom's half sister, same mother.
The second person shows as my first cousin as well. Based on some research I actually think she is my niece based on me being half siblings with her father. Can my test results tell me whether she is my 1st cousin or my niece?
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The 1st cousin heading on Ancestry DNA does not necessarily mean they are a first cousin, it only means that you share the amount of DNA with those people as a typical first cousin would. Ancestry does not list the full list of possible relationships, because that would take several paragraphs to do the full list in many cases.
Ancestry DNA only knows the amount of DNA you share with your matches. Except for very close relationships there are usually a number of possible relationships that could result in a similar amount of shared DNA.
I recommend using The Shared cM Project tool on DNA Painter. After entering 760 cM (or 744, the results are just about identical), it brings up a list of possible relationships. In the most probable category (86%):
Now it is up to you to determine the relationship based on the paper trail and/or other DNA matches. It sounds as though half aunt and half niece are the relationships you were expecting.
If there is still doubt over these relationships, consider DNA testing additional relatives such as your aunts or siblings. You would expect stronger DNA matches with these individuals.
I strongly recommend you get yourself and these folks on to Gedmatch.com. It's free. AncestryDNA does not have a chromosome browser and you really need that to see what is going on. If you have other people to compare to, that will be even better.
