People tell me I look like my father. I've never seen my dad, so does that mean I look invisible?

A sister can be seen as someone who is both ourselves and very much not ourselves - a special kind of double.

Grandmother pointed out my brother Perry, my sister Sarah, and my sister Eliza, who stood in the group. I had never seen my brother nor my sisters before; and, though I had sometimes heard of them, and felt a curious interest in them, I really did not understand what they were to me, or I to them. We were brothers and sisters, but what of that? Why should they be attached to me, or I to them? Brothers and sisters were by blood; but slavery had made us strangers. I heard the words brother and sisters, and knew they must mean something; but slavery had robbed these terms of their true meaning.

He felt like a brother of mine, but not at all like my actual brother. He seemed like someone I'd always know even if I never saw him again.

Because we all share an identical need for love, it is possible to feel that anybody we meet, in whatever circumstances, is a brother or sister. No matter how new the face or how different the dress and behavior, there is no significant division between us and other people. It is foolish to dwell on external differences, because our basic natures are the same.

Did you ever have a sister? did you?

If you have a sister and she dies, do you stop saying you have one? Or are you always a sister, even when the other half of the equation is gone?

Do I look dead to you?!

These people who have lost someone look naked because they think themselves invisible.

Your sister is the only true friend you'll ever have.

Oh, sister, am I not a brother to you
And one deserving of affection?
And is our purpose not the same on this earth
To love and follow his direction?
...
Oh, sister, when I come to knock on your door
Don't turn away, you'll create sorrow
Time is an ocean but it ends at the shore
You may not see me tomorrow

I thought the two ugly ones were sisters, but they got very insulted when I asked them. You could tell neither one of them wanted to look like the other one, and you couldn't blame them, but it was very amusing anyway.

Her eyes stare at me but she seems not to see me; she looks as though she were lost in her suffering.

I don't believe an accident of birth makes people sisters or brothers. It makes them siblings, gives them mutuality of parentage. Sisterhood and brotherhood is a condition people have to work at.