relationships are completely screwed up in TS4.
my sim had a daughter and then her husband died so
she got remarried and her new husband is not listed as
step-father just neighbor.
and she also has 6 kids. 2 of them are off and married with their own children,
the siblings don't come up as aunts and uncles only neighbors.
i hope they fix this soon!!
ESPECIALLY this,
if your sim dies, and then gets culled, forget any relationships you had,
they ALL UN-TIE. so siblings are no longer even related.