"My niece first called me "Daddy" at age 6.

Her father was notoriously extremely possessive and controlling.

At age 8 she had suicidal thoughts.

By age 10 she was trying to initiate a sexual relationship with me.

I know for sure I was a positive actor in her scenario. As is typically the case in romantic relationships, we seemed to sense out each other's unmet needs and find ways to meet them intuitively.

Anyway, there was something about my niece's relationship with her father (non-biological, by the way) that always put me on edge, for some reason I honestly couldn't put my finger on it.

My brother was a misogynistic, domineering dick. That much is certain."

"Since I came out to her parents, they have separated. My brother now lives in an apartment on his own.

I found out recently that her mother hits her when she's stressed. The same visit, I learned that my brother would no longer have sex with her."

Is your brother "extremely possessive and controlling", "a misogynistic, domineering dick" to your niece´s mother as well?

When she met him and got together with him, did she recognize that she wanted to be possessed and controlled by a misogynistic dick?

Has she had suicidal thoughts?
Has she tried to initiate a sexual relationship with any man other than your brother?