My older sister is my favorite person on the planet, by far.
My older sister and I are friendly, but I do not count her as a “friend”. A close acquaintance, maybe. She watches my kiddo sometimes, and we can have a reasonable conversation about random things (in a group, say at a family party). However, she and I don’t have any similar interests but one, never hang out for any particular reason, and we don’t seek out each other’s opinion on really anything.