Understanding DNA results?

Question

We are searching for my husband's father with nothing more than a name.

We did DNA through Ancestry and the person we thought would be his half-sister Person 1 came back as his first cousin 1,187 centimorgans shared across 43 DNA segments.

He also matched with a second cousin Person 2 292 centimorgans shared across 13 DNA segments. Person 2 matched Person 1 as 3rd cousin 129 centimorgan shared across 9 DNA segments.

What we know is Person 1's father who we thought was Person 3 father is cousin to Person 2's mother. Father and Mother both deceased were first cousins.

Trying to understand something that I know nothing about.

Is it possible Person 1 is Person 3's half sister?

Answer 1

1187 cM falls outside the bounds of the 99th percentile range for half siblings (1317 - 2312), but still has a positive probability. See: DNA Painter Shared cM Tool.

The age difference between your father and Person 1 may be important, because 1187 cM is smack dab in the middle of a half niece relationship. Perhaps Person 1's father is your father's half brother.