Determing if DNA match is half sibling or 1st cousin?

Question

The person in question matches a known aunt with 1718 cM and 56 segments. He matches a known 1st cousin with 967 cM and 49 segments.

He matches another relative with 2057 cM and 57 segments. Could he be a 1st cousin or half sibling with this data to this other relative?

The real question is which of two brothers are the father of this individual?

The 2057 cM and 57 segment match is on the son of one of the brothers (the other relative). The issue is neither of the brothers will take a DNA test so we hoped this reading of 2057 cM and 57 segments would be conclusive that he is a half sibling.

Is this possible to tell?

Answer 1

2057 cM is highly unlikely to be a first cousin; according to Blaine Bettinger's Shared cM Project, a first cousin is most likely within 553 - 1225 cM.

That high of a match fits into the grandparent, aunt/uncle, half-sibling, nibling, or grandchild relationship categories. See here: Shared cM Project with Relationship Probabilities for 2057 cM.

Can you use this information to solely determine the half-sibling status? No. But with the two other tests, I think it's solid.