Family comes in all shapes and sizes.
The "traditional" portrait of a father, mother, and kids erases a lot of different family structures, including LGBTQ parents, adopted families, chosen families, and families where various non-parental members become the sole guardians.
Frankly, how a family is structured is no one else's business, so long as there's safety and love - that's all that matters. Anyone who tries to "gotcha" someone about their family structure likely has some internal work to do.
He wrote:
AITA for telling my cousin to f**k off for trying to tell my brother I'm not his dad?
I (26m) have been raising my brother (7m) since he was a baby. Our parents died in an accident not long after he was born.